[BUG] Silent fails if other commits are added to the repo

[jayvdb]

Describe the bug
I manually added files to my emplace repo. emplace didnt detect its workarea is out of sync, and didnt report that it had failed to push the changes.

To Reproduce
Steps to reproduce the behavior:

1. Go to Github repo, add files manually
2. Install something locally that emplace will try to submit to repo
3. Check repo for new emplace addition

Expected behavior
emplace should either automatically detect that master has new changes, or fail so the user can manually rectify the conflict.