Return value of Filesystem::deleteDirectory(), deleteDirectories() and cleanDirectory()

[mlocati]

1. The Filesystem::deleteDirectory() method returns false if the directory does not exist, and true in any other cases.
   I think it should return false if the directory can't be deleted too.
2. Filesystem::deleteDirectories() returns false if the directory does not contain any sub-directories; shouldn't it return false if it can't delete these sub-directories? (and changing the return value to true if there's no directory to be deleted)
3. Filesystem::cleanDirectory() returns false if the directory does not exist, and true in any other cases.
   I think it should return false also if the directory hasn't been empties too.