FindGTK2: Add /usr/X11R6/ to include paths

Should fix builds on OpenBSD, see
http://open.cdash.org/viewTest.php?onlyfailed&buildid=3286713
Tests: Run RunCMake.target_compile_features unconditionally.

It is so far testing only cases which are fatal regardless of
recorded features.
Help: Add code example for INSTALL_INTERFACE to cmake-buildsystem.
Help: Link to cmake-buildsystem from CMP0052 docs.
ExternalData: Warn on missing file instead of failing

When the primary source tree path named by a DATA{} reference does not
exist, produce an AUTHOR_WARNING instead of a FATAL_ERROR.  This is
useful when writing a new DATA{} reference to a test reference output
that has not been created yet.  This way the developer can run the test,
manually verify the output, and then copy it into place to provide the
reference and eliminate the warning.

If the named source tree path is expected to be a file but exists as a
directory, we still need to produce a FATAL_ERROR.
Tests: Execute compile features tests unconditionally.

Conditionally create a dummy test if there are no known features.
Features: FATAL_ERROR on compilers with no recorded features.

Users of the new target_compile_features command are expected to
check the existence of the CMAKE_CXX_COMPILE_FEATURES variable before
attempting to use it to require features.
cmake: Print C++ stack trace after INTERNAL_ERROR messages

Since an INTERNAL_ERROR is always a bug, it will be useful to have the
program stack trace available in the report.
QtAutogen: Put generated qrc files in a target-specific dir.
CPackWIX: Delay creation of cmWIXPatch until CPack has initialized Logger

Without the fix CPack will crash when the cmWIXPatch class tries to issue
any diagnostics.
UseSWIG: Detect module name from interface file (#10080)

If no SWIG_MODULE_NAME is specified explicitly and the .i file exists,
scan it for the module name declaration.
UseSWIG: Revise and format documentation

Also add some documentation of SWIG_MODULE_NAME.
FindGTK2: Add GTK2_(FONTCONFIG|X11)_INCLUDE_DIR optional includes
Merge topic 'UseSWIG-guess_module_name'

2c96192f UseSWIG: Revise and format documentation
e147c5c5 UseSWIG: Detect module name from interface file (#10080)
Merge topic 'FindGTK2_fix_bsd'

d5a6069a FindGTK2: Add GTK2_(FONTCONFIG|X11)_INCLUDE_DIR optional includes
ef9366b0 FindGTK2: Add /usr/X11R6/ to include paths
Merge topic 'autorcc-target-dir'

33774ca2 QtAutogen: Put generated qrc files in a target-specific dir.
Merge topic 'internal-error-backtrace'

3de4c295 cmake: Print C++ stack trace after INTERNAL_ERROR messages
Merge topic 'CMP0052-docs'

692228e4 Help: Link to cmake-buildsystem from CMP0052 docs.
e5e9b8e9 Help: Add code example for INSTALL_INTERFACE to cmake-buildsystem.
Merge topic 'ExternalData-missing-not-fatal'

ccd29b9a ExternalData: Warn on missing file instead of failing
Merge topic 'fix-wix-cpack-crash'

cb59f5da CPackWIX: Delay creation of cmWIXPatch until CPack has initialized Logger