turns out it's not static after all :\

Revert "good grief why a proc it doesn't change"

This reverts commit 583c6e59eca018ca68e2dcdbc1f6ba5a1f62910c.

Conflicts:
	lib/bundler/source/git/git_proxy.rb
weirdest use of a closure ever

switch to an explicit circular reference, instead of an implicit
one via the closure. still not happy about it, though.