Update Chicken wip "development snapshot" package to stable release 4.8.0, while pkgsrc is still in freeze.

Changes since 4.7.0.6:

- Security fixes
  - improved hash table collision resistance and added randomization
    to prevent malicious external causes of collisions.  All SRFI-69
    procedures accept extra arguments to control randomization for
    testing/debugging.
  - Added checks for embedded '\0' characters in strings passed to some
    C functions on a lower level than Chicken's FFI.

- Build system
  - version information has been moved into a separate unit to make the
    build-version shown in the banner and accessible through library
    procedures more accurate, this also speeds up the build on version-
    changes (thanks to Jim Ursetto for contributing this)
  - the build was made more reliable with respect to cross-compilation
    and custom installation names
  - the test-suite is now working on the mingw32 platform (with
    a few tests disabled due to missing functionality)
  - the version and branch of the sources are now properly compiled
    into the core libraries and shown in the "csi" and "chicken"
    version headers

- Compiler
  - Fixed bug in handling of symbols in constant-definitions (thanks to Peter
    Bex)
  - Stricter check for value-part of constant definition (thanks to Kon Lovett)
  - Fixed bug that caused argument-signatures of external definitions to be
    incorrectly modified during optimization (thanks to Peter Bex)
  - Failing constant-folding expressions now produce a compile-time warning
  - Fixed various bugs in the internal type-database (thanks to Kon Lovett and
    Peter Bex)
  - added "-specialize" option and "specialize" declaration which enables
    optimizations of uses of core library procedures based on type-
    information gathered during flow analysis
  - "-optimize-level 3" and higher now implies "-specialize"
  - added option "-strict-types" and "-emit-type-file"
  - progress-information is now only shown with "-debug p"; the "-verbose"
    option only shows informational but noncritical messages
  - added optimizations for some library procedures
  - variable propagation for global variable accesses is now done in certain
    situations
  - the algorithmic complexity of the closure-conversion pass has been
    reduced which speeds up compilation noticably for large files
  - the alternative branch in a conditional is dropped when the condition
    is known to be a non-boolean value (suggested by Joerg Wittenberger)
  - implemented numerous fixes and improvements for flow analysis
  - fixed a bug in the compiler that could cause some variable bindings
    to be optimized away in certain situations involving inlining
  - added an experimental optimization called "clustering" (enable
    with the compiler option of the same name)
  - the optimizations done by the compiler are now listed as a comment
    in the generated C file
  - the type-information obtained during flow-analysis ("scrutiny") is
    now used for performing type-sensitive optimizations of calls to
    most of the core-library procedures
  - deprecated the "constant" declaration specifier
  - "unboxing" optimization has been completely removed - the implementation
    was unreliable and unmaintainable; the "-unboxing" compiler option will
    still be accepted but will produce a warning
  - Peter Bex contributed an optimization to the analysis pass that
    greatly reduces compile time for source code containing deeply nested
    lexical bindings
  - procedures that are known to have the value of a core library procedure
    that is a "standard" or "extended binding" will be inlined
  - enhanced line number tracking to get better error messages from
    the scrutinizer.
  - hygiene bugs related to compiler-syntax were fixed.
  - the local flow-analysis was sometimes reporting multiple warnings
    for the same type-conflict.
  - the time/space-complexity of some algorithms used in the compiler
    were reduced resulting in much better compile-times especially
    for large source files.

- Interpreter
  - ",q" leaves the currently active REPL invocation instead of
    terminating the process (as suggested by John Cowan)
  - ",m" properly switches between modules (thanks to Christian Kellermann)

- Core libraries
  - Cleaned up the set of available internal SRFI-feature-identifiers
  - The printer now does a better job at escaping certain single-character
    symbol names
  - Unit "lolevel"
    - deprecated "null-pointer" and "null-pointer?"
  - Disabled "-setup-mode" when compiling extensions for deployment (thanks
    to Ivan Raikov)
  - Got rid of some warnings in the C runtime system that were triggered on
    the SunPro C compiler (thanks to Joe Python)
  - added "foldl" and "foldr" procedures, which are more efficient and
    have a more consistent argument order than the corresponding
    SRFI-1 procedures
  - "shuffle" has been deprecated
  - added "queue-length"
  - "queue->list" allocates and returns a fresh list now
  - invoking a parameter-procedure with an argument will return the new
    value
  - added new procedure "quit"
  - "repl" accepts an optional evaluator procedure (suggested by John
    Cowan)
  - added a setter procedure to "signal-handler" ("posix" unit)
  - EINTR is properly handled for input routines that may block
    waiting for input
  - the implementation of R5RS evaluation environments is now fully
    standards compliant
  - "file-exists?" and "directory-exists?" work now properly for files
    > 2GB (EOVERFLOW handling in stat(3) system call)
  - fixed bug in implementation of "fifo?"
  - the procedure returned by "condition-predicate" accepts any type
    of argument now
  - blobs have a readable textual representation ("#{...}")
  - "find-files" does not follow symlinks by default (as it did previously)
  - also, the old non-keyword argument signature for "find-files" is not
    supported anymore
  - added "alist-update" ("data-structures" unit)
  - "irregex-replace" returns the original string instead of #f when the
    regex does not match
  - irregex "real" built-in utility pattern now accepts a leading sign
  - added "change-directory*" ("posix" unit)
  - number parsing has been made more reliable and standards compliant
  - deprecated "none?", "always?" and "never?"
  - library procedures that take ports as arguments now all perform checks
    on port-direction and open/closed state
  - "mutate-procedure" has been renamed to "mutate-procedure!" - the old
    name is still available but deprecated
  - deprecated C_hash_string and C_hash_string_ci functions in the C API in
    favor of the more secure versions C_u_i_string_hash, C_u_i_string_ci_hash
  - a number of bugs in the irregex regular expression engine have been
    fixed; it has been updated to upstream release 0.8.3
  - the "make" facility of the "setup-api" module has been deprecated,
    please use the "make" extension when your egg requires this during
    setup.

- Core tools
  - "csc"
    - The environment-variables "CHICKEN_C_INCLUDE_PATH" and
      "CHICKEN_C_LIBRARY_PATH" can now be used to add default include-
      and link-directories to C-compiler invocations
    - "-O5" passed expensive optimization flags to the C compiler which
      could expose C-Compiler bugs, depending on the compiler version
      (thanks to Sven Hartrumpf for pointing this out).
    - "-rpath" is ignored on OS X (thanks to Kon Lovett).
    - Fixed handling of "-output-file" (it was being ignored)
  - "chicken-install"
    - Added option "-override", which allows retrieving extension-
      versions from a file - this may be useful to ensure specific
      versions of a complete set of eggs are installed
    - Added option "-keep-installed"/"-x" that only installs explicitly
      named extensions given on the command line, if they are not
      already installed
    - Added option "-list" that lists all extensions available
    - Added option "-csi" to specify what interpreter should be used
      to execute the setup-script of an installed extension
    - Added option "-scan" that scans a local directory for the highest
      available extension versions available
    - Added option "-reinstall" that reinstalls all currently installed
      eggs, keeping their versions, if possible
    - Fixed bug with "chicken-install -test" when multiple extensions where
      given on the command line (thanks to Kon Lovett)
    - installing subdirectories works now on Windows.
    - fixed handling of "-force" when a "chicken" dependency version did
      not match
    - added new option "-show-foreign-depends" which lists foreign egg
      dependencies (if available)
    - added new option "-show-depends" which lists egg dependencies
    - added support for "or"-dependencies where a dependency is considered
      installed if one of a set of candidates is available
  - "chicken-profile"
    - fixed some bugs in the profiler and the runtime support code for
      profiling (thanks to Sven Hartrumpf)
  - "chicken-status"
    - Added option "-list" that dumps versions of installed extensions
      in a format suitable for "chicken-install -override ..."
    - the "pattern" argument is now actually treated as a pattern and not
      as a regex

- Core syntax
  - "assert" shows the line number of the form when a second argument
    is not given or is a literal string
  - "parameterize" now correctly omits invoking the guard procedure when
    the old value is restored (thanks to Joo ChurlSoo)
  - added ":", "the" and "assume" syntax for declaring types
  - added "define-specialization" form to declare type-driven procedure
    call rewrites in compiled code

- Syntax expander
  - Fixed a bug that caused imported identifiers to leak into the
    macroexpansion/compile-time environment (reported by Christian Kellermann)
  - Peter Bex fixed a bug that caused bound variables to be incorrectly
    renamed in quoted literals (thanks to Matthew Flatt)
  - fixed devious bug in the invocation and generation of transformer
    procedures
  - using normal "lambda" forms as transformers for local or global
    syntax definitions is deprecated - one should use "syntax-rules",
    "er-macro-transformer" or "ir-macro-transformer" from now on

- Runtime system
  - support for re-loading of compiled files has now been completely
    removed
  - the maximum length of strings is no longer limited to a 24-bit
    number on 64-bit architectures but can be 56 bits.
  - string-comparison handles embedded '\0' characters.
  - numerical predicates handle infinity and NaN correctly.
  - deprecated "[+-]nan", "[+-]inf" and other notations "accidentally"
    accepted by Chicken due to the underlying C library's strtod() function,
    standardizing on "[+-]nan.0" and "[+-]inf.0" from R6RS (and soon R7RS),
    when displaying numbers only these forms are generated now.
  - signals are queued to some extent and the interrupt handling has
    been cleaned up somewhat
  - the interpreter handles SIGINT directly - loading the "posix" unit
    is not needed anymore to handle this feature
  - changed default nursery size slightly and fixed a bug that caused
    incorrect (too small) nursery sizes on 64-bit platforms
  - deprecated the compiler option "-heap-initial-size", "-heap-growth"
    and "-heap-shrinkage"
  - the assembly-language stub routine for the implementation of "apply"
    was broken for Sparc64 systems and has been disabled for this platform
  - signal masks were accidentally reset upon GC for some platforms; use
    sigsetjmp/siglongjmp on BSD, Linux, MacOS X and Haiku

- Type system
  - added new type-specifiers "input-port", "output-port", "(list-of T)"
    and "(vector-of T)"
  - the type-specifiers "(vector T ...)" and "(list T ...)" represent
    fixed size lists and vectors now
  - added qualified types ("forall"), optionally with type constrains
  - added the "define-type" special form and type-abbreviations
  - added "compiler-typecase", a compile-time typematching form

- Module system
  - Added "interfaces", which are named groups of exports
  - Added "functors", which are parameterized modules
  - Modules can now be aliased
  - New syntax:
    (define-interface NAME EXPORTS)
    (functor (NAME ...) EXPORTS ...)
  - Extended syntax of "module" for aliasing and functor-instantiation
  - the "scheme" module has been integrated into the core library and
    is not installed as a separate import library anymore
  - added core module "r4rs" containing only bindings for R4RS identifiers
  - added core module alias "r5rs" for "scheme" module
  - added "module-environment" which returns an evaluation environment
    for the bindings of a module
  - fixed bugs related to using "export"/"reexport" in combination with
    wildcard ("*") module export lists (thanks to "megane")

- Foreign function interface
  - locatives are allowed as arguments declared "c-pointer"