git-p4: reduce number of server queries for fetches

git-p4: reduce number of server queries for fetches

When fetching changes from a depot using a full client spec, there
is no need to perform as many queries as there are top-level paths
in the client spec.  Instead we query all changes in chronological
order, also getting rid of the need to sort the results and remove
duplicates.

Signed-off-by: Sam Hocevar <sam@hocevar.net>
Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>