request-pull: avoid mentioning that the start point is a single commit

request-pull: avoid mentioning that the start point is a single commit

Previously we ran shortlog on the start commit which always printed
"(1)" after the start commit, which gives no information, but makes the
output less easy to read.  Instead of giving the author name of the
commit, use the space for committer timestamp to help recipient judge
the freshness of the offered branch more easily.

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>