Add support for dirFiles in FsMapper

[Kamil Breguła]

Hello,
Pig commands do not support all commands required by Oozie actions. We must come up with a better way to implement these tasks.

Thanks,

[Szymon Przedwojski]

Does the problem only apply to dir-files or are there more functionalities missing?
In any case, we can just describe it in the README for now and work on supporting it later.