The easiest way to do that is to rename the local branch after pushing.
This shows various levels of brokenness for the reset and rebase to upstream
commands: both menu entries display the wrong upstream branch name in the menu
(the local one rather than the remote one); executing the rebase command works
correctly though, the rebase command uses the right branch name. Resetting
fails, though.
We'll fix this in the next commit.
Put it into the individual menu items instead.
Again, this is necessary because we are going to add another entry to the menu
that is independent of the selected branch.
It is unexpected that a function called PushBranch also sets the upstream
branch; also, we want to add a PushBranch function in the next commit that
doesn't.
