Display underlying branch on prompt when remote is available

[calvn]

λ ~/.dotfiles/ on origin/master
$ git checkout -b master-local

λ ~/.dotfiles/ on master-local
$ git branch --set-upstream master-local origin/master

## Prompt is still origin master:
λ ~/.dotfiles/ on origin/master

## Want the following instead:
λ ~/.dotfiles/ on origin/master as master-local

[calvn]

Fixed in ce50b72