git p4: Squash P4EDITOR in test harness

If P4EDITOR is set in the environment, test behavior could be
unpredictable. Set it explicitly.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/lib-git-p4.sh b/t/lib-git-p4.sh
index b90986c2..121e380 100644
--- a/t/lib-git-p4.sh
+++ b/t/lib-git-p4.sh
@@ -24,6 +24,7 @@
 
 export P4PORT=localhost:$P4DPORT
 export P4CLIENT=client
+export P4EDITOR=:
 
 db="$TRASH_DIRECTORY/db"
 cli="$TRASH_DIRECTORY/cli"