CheckC*CompilerFlag: add documentation what to expect from a positive result
CPack: Fix a typo in documentation
OSX: Allow an empty INSTALL_NAME_DIR to override MACOSX_RPATH.

With this, projects can enable MACOSX_RPATH by default, but still have
a way to install libraries with no install name dirs into locations
such as /usr/local/lib by setting INSTALL_NAME_DIR="".
Fix OLD behavior of CMP0021.

Exclude Ninja and Xcode from the CMP0021 test

They do not behave the same as the makefile generator with
relative paths.

Don't overwrite the header file for in-source builds.
VS: Generate ToolsVersion matching each VS version

The MSBuild version for each Visual Studio generator isn't 4.0.  With
Visual Studo 2013 the ToolsVersion moved from being tied to the .NET
framework and now has its own version number.
Merge topic 'fix-OLD-CMP0021'

eef6df5 Fix OLD behavior of CMP0021.
Merge topic 'rpath-on-mac'

78cd884 OSX: Allow an empty INSTALL_NAME_DIR to override MACOSX_RPATH.
Merge topic 'doc-CPack-typo'

807a564 CPack: Fix a typo in documentation
Merge topic 'vs2013_toolset_14369'

3064f80 VS: Generate ToolsVersion matching each VS version
Merge topic 'doc-check-flags'

293ecfe CheckC*CompilerFlag: add documentation what to expect from a positive result