Merge branch 'jc/show-branch-g-current' into maint

The "--current" option of "git show-branch" should have been made incompatible with the "--reflog" mode, but this was not enforced, which has been corrected. source: <xmqqh76mf7s4.fsf_-_@gitster.g> * jc/show-branch-g-current: show-branch: -g and --current are incompatible