Improve Repository#log performance
Improve Repository#log performance

When `Repository#log` is called with a path option, compare commit trees
to determine if a commit changed the path instead of generating a diff
to make that determination.  Note that if the `:follow` option is also
passed, then `#log` falls back to using diffs since we rely on
`Rugged::Diff` to know if a commit renamed a file.

ontohub/gitlab_git,oliverguenther/gitlab_git,yukron/gitlab_git,gitlabhq/gitlab_git,sonalkr132/gitlab_git,argustelecom/gitlab_git,gitlabhq/gitlab_git,ontohub/gitlab_git,sadgb/gitlab_git,argustelecom/gitlab_git,Datacom/gitlab_git,flycutter/gitlab_git,yehaha9876/gitlab_git,jvanbaarsen/gitlab_git,flycutter/gitlab_git