MR on Fork multiple fixes

-Disable observers post test run
-Allow db:seed_fu RAILS_ENV=test to be run more than once without error
-fix diffs_in_between, was passing in the default_options for grit, but grit in this case doesn't take options, fixed the test to actually fail if the incorrect diffs are returned
-make notes/commits render against proper project
-MR discussion file links should reference note's project
-Added tests for commit links on edit merge request
-fixes edit issues (canceling an edited mr, updating an edited mr)
-updates tests with checks for source code updates
-still forked_merge_requests.feature (project_forked_merge_requests) test not passing (commented out -- "stable" not being set)

MR API: error on bad target_project

-If the target project id is specified and it is not the same as the project the request is being made on (the source), and the it isn't a fork of that project, error out, otherwise use it as the target
-Fixes some busted (but hidden) test cases

Conflicts:
	app/views/merge_requests/show/_diffs.html.haml
	spec/features/notes_on_merge_requests_spec.rb

Change-Id: I20e595c156d0e8a63048baaead7be6330c738a05