git-p4: keyword flattening fixes

git-p4: keyword flattening fixes

Join the text before looking for keywords.  There is nothing to
prevent the p4 output marshaller from splitting in the middle of a
keyword, although it has never been known to happen.

Also remove the (?i) regexp modifier; perforce keywords are
documented as case-sensitive.

Remove the "\n" end-character match.  I don't know why that is
in there, and every keyword in a fairly large production p4 repository
always ends with a $.

Acked-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>