Micro-optimization to scm_i_vm_mark_stack

* libguile/vm.c (scm_i_vm_mark_stack): Micro-optimize GC_MARK_AND_PUSH
  to cache the plausible heap bounds locally.
Return unused parts of the stack to the OS

* libguile/vm.h (struct scm_vm): Reorder fields.  Add "sp_max_since_gc"
  field.
* libguile/vm-engine.c (ALLOC_FRAME, RESET_FRAME):
* libguile/vm.c (vm_return_to_continuation)
  (vm_reinstate_partial_continuation, scm_call_n): In places where we
  could increase the stack height, update sp_max_since_gc.
  (vm_expand_stack): Relocate sp_max_since_gc on expansion.
  (scm_bootstrap_vm): Record the page size using gnulib's getpagesize.
  (return_unused_stack_to_os): New routine, run when marking stacks.
Add dead slot map cache

* libguile/vm.c (find_dead_slot_map, scm_i_vm_mark_stack): Use a little
  cache for dead slot maps.  Helps when marking very deep recursive
  stacks.
Add thread-local lock-free, TLS-free freelists.

* libguile/bdw-gc.h: Remove a needless compatibility hack.

* libguile/gc-inline.h: New file, implementing thread-local freelists
  providing faster allocation if we already have a scm_i_thread*
  pointer.  Based on gc_inline.h from libgc.

* libguile/threads.h (scm_i_thread): Add freelists here.
* libguile/threads.c (guilify_self_1, guilify_self_2): Initialize
  freelists.

* libguile/vm.c: Include gc-inline.h.
* libguile/vm-engine.c: Rename current_thread to thread.  Use
  scm_inline_cons instead of scm_cons, scm_inline_cell instead of
  scm_cell, and scm_inline_words instead of words.
Remove code to run GC more frequently as process image size increased

* libguile/gc.c: Remove code that would try to run GC more frequently as
  the process image size was increasing.  Before, it was often the case
  that the heap was the main component of image size, but with
  expandable stacks and statically allocated data that is no longer
  true.  Also, once scm_gc_register_allocation was incorporated, we
  don't need to be so conservative any more.  It seems this code was
  simply causing too many gc's to run.  Removing it improves some
  micro-benchmarks; time will tell.
Add VM and compiler support for calls to known procedures

* module/language/cps.scm ($callk): New expression type, for calls to
  known labels.  Part of "low CPS".
* module/language/cps/arities.scm:
* module/language/cps/closure-conversion.scm:
* module/language/cps/compile-bytecode.scm:
* module/language/cps/dce.scm:
* module/language/cps/dfg.scm:
* module/language/cps/effects-analysis.scm:
* module/language/cps/simplify.scm:
* module/language/cps/slot-allocation.scm:
* module/language/cps/verify.scm: Adapt call sites.

* libguile/vm-engine.c (call-label, tail-call-label): New instructions.
  Renumber the rest; this is an ABI change.

* libguile/_scm.h (SCM_OBJCODE_MINOR_VERSION):
* module/system/vm/assembler.scm (*bytecode-minor-version*): Bump.

* doc/ref/compiler.texi (CPS in Guile): Document $callk.
Various VM stack management fixes

* libguile/vm.c (vm_increase_sp): New interface, to increase the SP to
  some new level, possibly expanding the stack.
  (vm_push_sp, vm_restore_sp): Intefaces to vm_increase_sp.
  (vm_return_to_continuation): Don't throw an error if there's not
  enough space; instead, expand.
  (vm_reinstate_partial_continuation): Use the new helper.
  (return_unused_stack_to_os): Avoid off-by-one error (sp points to
  valid memory.)
  (scm_call_n): Never write beyond the sp.
Tests for array-copy!, empty case

* test-suite/tests/ramap.test: test array-copy! with empty destination.
  Fix uses of constant array as destination.
Replace scm_c_generalized_vector_length in random.c

* libguile/random.c: (random:solid-sphere!): array is of known
  rank 1, so use scm_c_array_length() instead.
Replace scm_c_generalized_vector_length in arrays.c

* libguile/arrays.c: (scm_array_contents, scm_make_shared_array):
  arrays are known of rank 1 so replace by scm_c_array_length.
Replace generalized-vector calls in array_handle_ref/set

* libguile/arrays.c: (array-handle-ref, array-handle-set): Use the
  rank-1 array accessors.
Don't use generalized-vector functions in uniform.c

* libguile/uniform.c (scm_is_uniform_vector): Replace
  scm_is_generalized_vector and scm_generalized_vector_get_handle by
  scm_is_array and manual rank check.
  (scm_c_uniform_vector_length): Use scm_c_array_length.
  (scm_c_uniform_vector_ref): Use scm_c_array_ref_1.
  (scm_c_uniform_vector_set): Use scm_c_array_set_1_x.
  (scm_uniform_vector_writable_elements): Use scm_array_get_handle, and
  assert that the rank is 1.

* test-suite/test/arrays.test: Rename the uniform-vector-ref block to
  uniform-vector.  Exercise uniform-vector-length and shared arrays
  remaining uniform.

Modifications by Andy Wingo <wingo@pobox.com>.
Don't use generalized-vector in array-map.c (I)

* array-map.c: (AREF, ASET): Rename from GVREF, GVSET and use rank-1
  array accessors.
Don't use generalized-vector in array-map.c (II)

* libguile/array-map.c
  - replace scm_is_generalized_vector by scm_is_array && !SCM_I_ARRAY_P.
  - replace scm_c_generalized_vector_length by scm_c_array_length.
  - remove header.
Array-map refactors

* libguile/array-map.c (scm_ra_matchp): Refactor logic a bit.
  (array_index_map_1, array_index_map_n)
  (scm_array_index_map_x): Internally refactor array-index-map! to use
  separate implementations for rank 1 versus rank >1 arrays.
Fix array-index-map refactor

* libguile/ramap.c (array_index_map_1): Fix to use array handle
  properly.
Remove generalized-vectors.h includes

* libguile/srfi-4.c, libguile/uniform.h: ditto.
Remove unnecessary conditions in array constructors

* libguile/arrays.c: (scm_make_type_array, scm_from_contigous_typed_array,
  scm_from_contigous_array): Remove conditions known to be true.
Tests for shared-array-root

* test-suite/tests/arrays.test: check shared-array-root against
  make-shared-array, array-contents.
Don't use scm_is_generalized_vector in shared-array-root

* libguile/arrays.c: (scm_shared_array_root): replace check for
  scm_is_generalized_vector.