Merge Request dependencies

If you are working on a project, it may occur that you are working on an extension of a branch that is currently in review as a merge request (MR), but essentially feature-complete.

It'd be nice if any new MR that has the full initial commitset of another open MR would get annotated as 'depends on Merge Request #x', so that it does not get merged before the parent MR, and that it is clear that some branches are dependent on eachother.

When this feature is implemented, in the diff view then it should give you the option to display the diff on the base branch, but also just the diff made in only this merge request, taking out the changes made in the parent branches.

Features:

Let base be the base branch to which the MRs are made.
Let A be a merge request to be merged into base.
Let B be a new merge request that is based on A, or has the changeset of A contained within its own changeset, but wants to be merged into base.

• When B is made, its page states This merge request depends on 'A', and A's page states This merge request is built upon by 'B'
• When A gets updatet by another commit, this is visible on B's page as This merge request depends on 'A', and is [x] commits behind
• In the diff view of B, it should only display the changes made by B, as the changes that came from A are visible in that MR. This can also be an option, or a checkbox in the view.