Fix potentially dangerous uses of mkpath and git_path

Replace them with mksnpath/git_snpath and a local buffer
for the resulting string.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-apply.c

@@ -2850,8 +2850,8 @@ static void create_one_file(char *path, unsigned mode, const char *buf, unsigned
 		unsigned int nr = getpid();
 
 		for (;;) {
-			const char *newpath;
-			newpath = mkpath("%s~%u", path, nr);
+			char newpath[PATH_MAX];
+			mksnpath(newpath, sizeof(newpath), "%s~%u", path, nr);
 			if (!try_create_file(newpath, mode, buf, size)) {
 				if (!rename(newpath, path))
 					return;