git p4 test: start p4d inside its db dir

This will avoid having to do native path conversion for
windows.  Also may be a bit cleaner always to know that p4d
has that working directory, instead of wherever the function
was called from.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-git-p4.sh

@@ -40,8 +40,11 @@ start_p4d() {
 	mkdir -p "$db" "$cli" "$git" &&
 	rm -f "$pidfile" &&
 	(
-		p4d -q -r "$db" -p $P4DPORT &
-		echo $! >"$pidfile"
+		cd "$db" &&
+		{
+			p4d -q -p $P4DPORT &
+			echo $! >"$pidfile"
+		}
 	) &&
 
 	# This gives p4d a long time to start up, as it can be