Don't run the ssh clone tests against http remotes
Remove the refs/notes/commits that we push in test

The online::push::notes test pushes a note but leaves it hanging
around for other tests to stumble across when they're validating
that they're seeing the refs they expect to see.  Clean it up on
exit.
Free references during push validation
online::clone::credentials support default credentials
Perform HTTP keep-alive
Introduce git_buf_decode_base64

Decode base64-encoded text into a git_buf
Add GSSAPI support for SPNEGO/Kerberos auth over HTTP
Introduce proper http authentication API
Merge pull request #2497 from ethomson/kerberos3

SPNEGO authentication via GSSAPI