Remove all subshells from VCS functions
Remove all subshells from VCS functions

This is getting close to good on the subshell front. A lot of work to be
done on a normal API for the VCS providers instead of a monster like
_lp_git_branch_color().

jaesivsm/liquidprompt,nojhan/liquidprompt,pkkolos/liquidprompt,milouse/liquidprompt,laurentbardin/liquidprompt