The "--head" option to "git show-ref" was only to add "HEAD" to the
list of candidate refs to be filtered by the usual rules
(e.g. "--heads" that only show refs under refs/heads). Change the
meaning of the option to always show "HEAD" regardless of what
filtering will be applied to any other ref (this is a backward
incompatible change, so I may need to add an entry to the Release
Notes).
* db/show-ref-head:
show-ref: make --head always show the HEAD ref