Be more lenient when there are multiple merge bases

[jjlharrison]

Background

There can be multiple merge bases with a given branch. This can mean that you can find yourself in the situation where the coverage plugin selects a merge base that does not include changes that were introduced later in that same branch. Example;

1. Branch off develop and make changes.
2. Take an earlier branch from develop (a hotfix for example) and merge it into your new branch.

If the merge base is selected from the earlier hotfix you may find that the coverage plugin wants you to write coverage for changes in develop. This may be implausible.

Solution

Do not select a single merge base. Collect all of them, check the diffs and coverage for each, and then use the most lenient for enforcing coverage.