Fixed big flaw in vtkCleanFolder.

- FileSystemObject.DeleteFolder needs a path as a parameter, and the
  Force:=True parameter to function properly.
  It is now a dangerous function as it forces deletion.

- Not sure why the tests were working as they were relying on the
Folder.Subfolders.Count method, the same I used when debugging.

- Implemented proper error tracking in vtkGitFunctionsTester. Will keep
  doing that systematically in the future as it drastically eases the bug hunt.
Added tests for git.

Tests failing (createProject not updated).
GitFunctions finished.

- vtkMainFunctions
	- added Git support

- vtkCreateFolderTester
	- added a test for git support

- vtkFileSystemUtilities
	- removed vtkCreateTreeFolderWithGitIgnore

- vtkCreateTreeFolderTester
	- removed test of vtkCreateTreeFolderWithGitIgnore

- vtkGitFunctions
	- added .git/info/exclude update in vtkInitializeGit

- vtkGitFunctionsTester
	- added .git/info/exclude tests

- removed .gitignore and updated .git/info/exclude