Merge commits should also be matched (indicated by a '-') for the case
that the base branches last commit is a merge commit and another branch
exists that checked out the newest commit that was merged.
Example log (from `glog`):
```
* abcdef Foo (HEAD -> feature)
* bcdefa Merge branch 'other-feature' into base (base)
|\
| * cdefab Bar (other-feature)
|/
* ...
...
```
with `git show-branch -a` output like:
```
! [base] Merge branch 'other-feature' into base
* [feature] Foo
! [other-feature] Bar
---
* [feature] Foo
-- [base] Merge branch 'other-feature' into base
+*+ [other-feature] Bar
```
Here we want `base` to be returned instead of `other-feature` and thus
'-' needs to be matched as well.
druckdev
c1955dd5f5
