vtkCleanFolder : back to FileSystemObject

vtkConstants
- added constant VTK_RETVAL_UNEXPECTED_ERROR = 2000

vtkFileSystemUtilities
- added function vtkCleanFolder_Dir that doesn't work
- vtkCleanFolder is now with FileSystemObject
In vtkGitFunctions : updated check of Git install
Updated vtkInitializeGit.

- 2 optional arguments : textLogFolderName and textLogFolderPath
- Cleaner Shell calls
	- no "cd"
	- "/c" instead of "/k"
- addedFunction vtkGitConvertWinPath