xdiff: avoid signed vs. unsigned comparisons in xpatience.c

The loop iteration variable is non-negative and used in comparisons
against a size_t value. Use size_t to eliminate the mismatch.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

xdiff/xpatience.c

@@ -20,8 +20,6 @@
  *
  */
 
-#define DISABLE_SIGN_COMPARE_WARNINGS
-
 #include "xinclude.h"
 
 /*
@@ -78,7 +76,7 @@ struct hashmap {
 
 static int is_anchor(xpparam_t const *xpp, const char *line)
 {
-	int i;
+	size_t i;
 	for (i = 0; i < xpp->anchors_nr; i++) {
 		if (!strncmp(line, xpp->anchors[i], strlen(xpp->anchors[i])))
 			return 1;