Fix ref parsing in Gitlab::GitAccess
Fix MR commenting system when new commits pushed

This conmmit fixes wierd behaviour when you see wrong comments about new
commits in merge requests.

Short explanation of a bug:
When you push new commits to project we updated `project.merge_requests`
with comment about push. But `project.merge_requests` includes also
merge requests from forks to origin project. So when you push to master
branch it commented on all merge requests from forks to origin where
source_branch was `master`
Fix 500 error on diff if file permission changed
Prevent 500 error on search results if description contains relative link
Add fixes to changelog
Version 7.3.1