name-rev: don't leak path copy in name_ref()

name-rev: don't leak path copy in name_ref()

name_ref() duplicates the path string and passes it to name_rev(), which
either puts it into a commit slab or ignores it if there is already a
better name, leaking it.  Move the duplication to name_rev() and release
the copy in the latter case.

Signed-off-by: René Scharfe <redacted>
Signed-off-by: Junio C Hamano <redacted>