CMP0054: Remove ALLOWED_UNKNOWN_VARIABLE_READ_ACCESS

The CMake code for it is now redundant and only slows down uninitialized
variable accesses.
tests: test CMP0054
CMake Nightly Date Stamp
Merge topic 'compile-features-C-language'

e0890d03 Features: Extend concept to C language.
Merge topic 'preserve_cmake_minimum_required_version'

1890c668 Keep cmake_minimum_required calls in sync with current version
81a3f228 Do not change minimum required version in modules
Merge topic 'test-BuildDepends-sleep'

e4114ee9 Tests/BuildDepends: Make 3-second delay more robust
Merge topic 'update-kwsys'

2903d609 Merge branch 'upstream-kwsys' into update-kwsys
ed52685d KWSys 2014-05-19 (c282e64f)
Merge branch 'master' into next
KWSys SystemTools: Port cygwin path conversion to modern API

The cygwin_conv_to_win32_path function is deprecated in favor of
cygwin_conv_path.  Use the latter.
KWSys Process: Workaround child kill trouble on Cygwin

When we kill a child we send SIGSTOP first so that we can traverse its
child processes recursively.  On unwinding the recursion we then send
SIGKILL.  Current Cygwin has trouble when both signals are sent in quick
succession by the parent process.  Add a usleep(1) after sending the
first signal to give up our time slice and give Cygwin a chance to
process the first signal before sending the second.
Features: Record for Clang 3.4

Clang 3.4 supports all features currently known to CMake.
Merge topic 'clang-features' into next

cda23319 Features: Record for Clang 3.4
cmMakefile: Extract CompileFeatureKnown method.
cmMakefile: Extract CompileFeaturesAvailable method.
cmMakefile: Add methods for checking availability of a feature.
cmMakefile: Extract CheckNeeded{C,Cxx}Language methods.
Features: Add COMPILE_FEATURES generator expression.

Allow setting build properties based on the features available
for a target.  The availability of features is determined at
generate-time by evaluating the link implementation.

Ensure that the <LANG>_STANDARD determined while evaluating
COMPILE_FEATURES in the link implementation is not lower than that
provided by the INTERFACE of the link implementation.  This is
similar to handling of transitive properties such as
POSITION_INDEPENDENT_CODE.
Merge topic 'COMPILE_FEATURES-genex' into next

bb1c0b63 Features: Add COMPILE_FEATURES generator expression.
9939cb53 cmMakefile: Add methods for checking availability of a feature.
b6dedf03 cmMakefile: Extract CheckNeeded{C,Cxx}Language methods.
8dd129df cmMakefile: Extract CompileFeaturesAvailable method.
6b9b2fff cmMakefile: Extract CompileFeatureKnown method.
Features: Ensure that list exists to remove from.
Help: Fix whitespace in doc link.