error callback for failed study GET.
dealing with the pair (sha, data) from study GET

Not using the SHA1 when posting edits, but
not crashing on the new GET return.
Merge branch 'master' into sha-bookkeepping

Conflicts:
	curator/static/js/study-editor.js
Fix bad merge. Stash & resend starting_commit_SHA.

Now we capture the most recent commit SHA when GETting a study, and
provide this as query-string var 'starting_commit_SHA' when PUTting it
back to the repository.