In a repository with mainto/1.0 (to keep maintaining the 1.0.X
series) and fixo/1.0 (to keep fixes that apply to both 1.0.X
series and upwards) branches, "git-name-rev mainto/1.0" answered
just "1.0" making things ambiguous.  Show refnames unambiguously
like show-branch does.
Signed-off-by: NJunio C Hamano <junkio@cox.net>