Add STASH_REPO_NAME and STASH_IS_ADMIN to the hook environment

[rappazzo]

I was looking to use these in my external hooks: • STASH_REPO_NAME - useful for logging and for rejected push responses. • STASH_IS_ADMIN - useful for allowing certain users to push by permission (in some cases)

I did not bump the revision in the pom.xml file.

[seletskiy]

That's great! Thanks!