pathspec: match and original in pathspec_item are const

No existing code modifies these two strings in pathspec elements
after they are created via these two pointers.  Declare them as
"const char *" to stress on this fact and cast away constness from
the code that frees these two strings.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

pathspec.c

@@ -749,8 +749,8 @@ void clear_pathspec(struct pathspec *pathspec)
 	int i, j;
 
 	for (i = 0; i < pathspec->nr; i++) {
-		free(pathspec->items[i].match);
-		free(pathspec->items[i].original);
+		free((void *)pathspec->items[i].match);
+		free((void *)pathspec->items[i].original);
 
 		for (j = 0; j < pathspec->items[i].attr_match_nr; j++)
 			free(pathspec->items[i].attr_match[j].value);

pathspec.h

@@ -35,8 +35,8 @@ struct pathspec {
 	unsigned magic;
 	int max_depth;
 	struct pathspec_item {
-		char *match;
-		char *original;
+		const char *match;
+		const char *original;
 		unsigned magic;
 		int len, prefix;
 		int nowildcard_len;