Shouldn't supply a response body to Git clients when returning 401 response

A reported a problem with cloning repositories via HTTP with recent versions of Git.

Either due to a change in git or a particular version of libcurl git was compiled against the Not Authenticated String Stash sends back to the client causes git to not identify the repository as supporting the smart HTTP protocol.

Symptoms: a clone attempt aborts with

fatal: http://user@example.com:7990/scm/PROJECT/repo.git/info/refs not valid: is this a git repository?

To workaround this problem, Stash should supply an empty response body when returning a 401 to the git client.