Creating a new branch fails if current branch does not exist on the remote

[isc-pbarton]

If I create a new branch locally, never push that branch to the remote, and then try to create another new branch, it fails with an error "There is no tracking information for the current branch."
It fails because we issue a "git pull" before creating the new branch.
This is a regression caused by #625 - previously, the pull would fail silently.
We should revisit whether we actually want to do a pull before creating a new branch.

[isc-pbarton]

Actually, we only do the pull if we are in basic mode and the default merge branch is set. We do want to throw an error here if the default merge branch doesn't exist on the remote. So current behavior is as expected.