name-rev: allow to specify a subpath for --refs option

name-rev: allow to specify a subpath for --refs option

When an user wants to filter specific ref using the --refs option,
the pattern needs to match the full ref, e.g. --refs=refs/tags/v1.*.

It'd be convenient to specify a subpath of ref pattern.  For
example, --refs=origin/* can find refs/remotes/origin/master by
searching the pattern against its substrings in turn:

  refs/remotes/origin/master
  remotes/origin/master
  origin/master

If it finds a match in a subpath, unambigous part of the ref path will
be removed in the output.

Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>