Move ref path matching to connect.c library

It's a generic thing for matching refs from the other side.

cache.h

@@ -261,6 +261,7 @@ struct pack_entry {
 
 extern int git_connect(int fd[2], char *url, const char *prog);
 extern int finish_connect(pid_t pid);
+extern int path_match(const char *path, int nr, char **match);
 
 extern void prepare_packed_git(void);
 extern int use_packed_git(struct packed_git *);