pull requests: default target branch

[Thomas De Schampheleire]

Hi,

When creating a pull request in Kallithea, the tip (or specified
revision) in the originating repository is compared with the
destination repo's tip.

When having several release branches, this choice could be confusing:
suppose someone makes changes on the default branch and creates a pull
request. If the last change in the target repo happens to be on the
branch of another release, the list of revisions is huge. The creator
of the pull request may not immediately realize that he should select
the default branch explicitly.

There already exists the concept of 'landing revision' but it does not
seem to be used here. A proposal is:
- for the source, use the current tip (this is typically the change of
the developer)
- for the target, use the landing revision (which could be changed to
the default branch in my case).

An alternative is:
- for the source, use the current tip (this is typically the change of
the developer)
- for the target, use the same branch as the source is on, if it
exists, otherwise use the landing revision (or the current tip).

Other ideas?

Thanks,
Thomas