feat(git): gate visible-tabs hack behind an environment variable
feat(git): gate visible-tabs hack behind an environment variable

Because it is a bit too intense, and I think I'm going to want to break
it out only in special cases.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent