Features: Add support for C++14 features.

Record the features implemented by GNU 4.9 and Clang 3.4.
FindDoxygen: Improve search for Graphviz "dot" on Windows

As of Graphviz 2.31, their installer provides no PATH or registry
modifications.  Glob possible install paths instead.

Inspired-by: Lars Bilke <larsbilke83@googlemail.com>
FindDoxygen: Deprecate DOXYGEN_DOT_PATH

While at it, do not cache the value since it should always be
computed directly from DOXYGEN_DOT_EXECUTABLE.

Inspired-by: Lars Bilke <larsbilke83@googlemail.com>
CPackDeb: Invoke "dpkg-shlibdeps --version" with C locale

The version message is localized and may not match when a non-english locale is in use.
add_custom_command: Normalize OUTPUT and DEPENDS paths.

While tracing dependencies of a target, cmTargetTraceDependencies
follows sources by full path to determine if the source is to be
produced by a custom command.  Commit 4959f341 (cmSourceFileLocation:
Collapse full path for directory comparisons., 2014-03-27) changed
the storage of target sources to be in the form of a normalized
path instead of an unnormalized path.

The path is followed by looking it up in a mapping via
cmMakefile::GetSourceFileWithOutput to acquire an appropriate
cmSourceFile.  The mapping is populated with the OUTPUT components
of add_custom_command invocations, however it is populated with
unnormalized paths.  This means that the tracing logic does not
find appropriate cmSourceFiles, and does not generate appropriate
build rules for the generated sources.

Normalize the paths in the OUTPUT components of add_custom_command
to resolve this.

The paths in the DEPENDS component of add_custom_command are also
not normalized, leading to the same problem again.  Normalize the
depends paths after generator evaluation and expansion.
VS: Use lower-case boolean values in VS 7-9 (#14927)

The VS 7-9 IDEs parse .vcproj file boolean values in lower or upper
case.  The .NET XML parsing chokes on anything but "true", "false", "0",
"1".  Teach our generators to use lower-case names since they will work
for both parsers.  Our VS >= 10 flag tables already use lower-case.
Merge topic 'cxx14-features'

dd043c3f Features: Add support for C++14 features.
Merge topic 'FindDoxygen-windows-dot'

f49b6a33 FindDoxygen: Deprecate DOXYGEN_DOT_PATH
7980eab8 FindDoxygen: Improve search for Graphviz "dot" on Windows
Merge topic 'vs-vcproj-bool-case'

b684ce58 VS: Use lower-case boolean values in VS 7-9 (#14927)
Merge topic 'dpkg-shlibdeps-locale'

21ec5f84 CPackDeb: Invoke "dpkg-shlibdeps --version" with C locale
Merge topic 'normalize-custom-command-paths'

c4af46b4 add_custom_command: Normalize OUTPUT and DEPENDS paths.