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.
CMake 3.0.0-rc4
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.
CMake Nightly Date Stamp
Utilities/Sphinx: Port documentation generation to python3 (#14886)
Merge topic 'sphinx-python3'

69069cfb Utilities/Sphinx: Port documentation generation to python3 (#14886)
Merge branch 'sphinx-python3' into release
Merge branch 'release'
QtAutogen: Put generated qrc files in a target-specific dir.
Merge branch 'release'
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.
CMake Nightly Date Stamp
CMake Nightly Date Stamp
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