Add Generation and Metageneration to gsutil stat output.

Right now, it is not possible for developers to atomically get
the generation or metageneration, since gsutil ls -la is not
atomic. Add this info to gsutil stat output to resolve this problem.

This change has the side effect of adding the same output
to gsutil ls -L output.
Merge pull request #159 from davidjamesca/master

Add Generation and Metageneration to gsutil stat output.