- Added #deleteIfAbsent: , #ensureDeleted and #ensureClosed.
- Added #testDeleteIfAbsent, #testEnsureClosed, #testEnsureDeleted and #testExists.
- Make FileSystemHandleTest  >> tearDown more robust by using ensure* methods. 

I have know much about FileSystem so if someone can check please. I don't know if the classes where I place the unit tests are the correct place.


http://code.google.com/p/pharo/issues/detail?id=6060

thanks