Call strbuf_add_unique_abbrev() to add an abbreviated hash to a strbuf
instead of taking a detour through find_unique_abbrev() and its static
buffer. This is shorter and a bit more efficient.
Patch generated by Coccinelle (and contrib/coccinelle/strbuf.cocci).
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>