Check explicitly that path is absolute.

Otherwise we can confuse usual includes with automatic ones.
SVN_SILENT made messages (.desktop file)
Allow only 3 arguments to cmake command set_property

The llvm cmake build system generates (among others) this line:
set_property(GLOBAL PROPERTY LLVMBUILD_LIB_DEPS_LLVMSupport )
set_property only has 3 arguments which is fine, even cmake documentation for this command says the value is optional.

REVIEW: 116897
SVN_SILENT made messages (.desktop file)
First attempt on splitting Custom Build System into 2 parts.
Fix issue when converted settings were not written.
Also add all parent's includes/defines.
Add more test cases.
Don't replicate defines.
Beautify code slightly.
Add thread synchronization just in case.
Add IDefinesAndIncludesManager interface.
Port CustomDefinesAndIncludesManager to the interface.
Futher code clean up.
Move IncludesAndDefines plugin into language folder.
Add tests for the plugin.
Bring back some debug. Add missing files.
Remove some unused code/files. Fix copyright issues.
Test clean up.
Add support for auto includes.