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: <redacted>

* jc/show-branch-g-current:
  show-branch: -g and --current are incompatible

diff --cc builtin/show-branch.c
Simple merge