Remove .vim directory if it is not manged by pivotal_workstation

If you use vim before running pivotal_workstation, git will refuse to
take over the .vim directory.  Fixes Issue 246.
Merge branch 'master' of git://github.com/pivotal/pivotal_workstation
Fail if .vim directory is not manged by pivotal_workstation

If you use vim before running pivotal_workstation, vim will create a
.vim directory, which git will refuse to take over.  Fixes Issue 246.
Split vim and vim_config recipes

The vim_config recipe raises an error if the user is unwilling to cede
control of the .vim directory.  Splitting the recipes lets those users
avoid the error by excluding the vim_config recipe.  They can still
install vim by including the vim recipe.
Maybe satisfy foodcritic?
More appeasing the critics.
Merge branch 'pr/256'