Don't require equivalent repositories.

Repository equivalence is Tricky® and if we can’t diff, we’ll find out
from libgit2.
Merge pull request #332 from libgit2/dont-require-same-repository

Don't require equivalent repositories.
Merge remote-tracking branch 'origin/master' into filter-lists
Clarify why both a path and blob are provided
Take ownership of the loaded git_filter_list