Try to look up a fork by name before getting all forks
Add check to user_has_fork_of_repo? for the case when no forks exist
Add check to user_has_fork_of_repo? for the case when we should get the repo's forks
Merge pull request #1 from jdennes/better-has-forked-check

Optimise checking done in ContributionChecker::Checker#user_has_fork_of_repo?