Use PATH_MAX instead of MAXPATHLEN

According to sys/paramh.h it's a "BSD name" for values defined in
<limits.h>. Besides PATH_MAX seems to be more commonly used.

Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/builtin-checkout-index.c b/builtin-checkout-index.c
index 6b55f93..b097c88 100644
--- a/builtin-checkout-index.c
+++ b/builtin-checkout-index.c
@@ -45,7 +45,7 @@
 static int line_termination = '\n';
 static int checkout_stage; /* default to checkout stage0 */
 static int to_tempfile;
-static char topath[4][MAXPATHLEN+1];
+static char topath[4][PATH_MAX + 1];
 
 static struct checkout state;