Merge branch 'ab/mktag-tests'

Fill test gaps. * ab/mktag-tests: mktag tests: test fast-export mktag tests: test for-each-ref mktag tests: test update-ref and reachable fsck mktag tests: test hash-object --literally and unreachable fsck mktag tests: invert --no-strict test mktag tests: parse out options in helper