cmDependsC: Collapse relative include paths

While calculating dependencies collapse sequences such as

 ../../../a/b/c/../../d/e/../../e/f

to avoid total path lengths over the Windows path length limit as much
as possible.
FindGTK2: Do not fail on MSVC11 if vc100 libraries are available
Merge topic 'make-depends-collapse-paths'

551d334 cmDependsC: Collapse relative include paths
Merge topic 'FindGTK2vs11'

eb16301 FindGTK2: Do not fail on MSVC11 if vc100 libraries are available