Replace most uses of strncmp() with prefixcmp()

This is a preparation for replacing all prefix checks with either
strip_prefix() or starts_with() when Git 1.8.6 is released.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>

scan-tree.c

@@ -105,7 +105,7 @@ static void add_repo(const char *base, struct strbuf *path, repo_config_fn fn)
 		return;
 	strbuf_setlen(path, pathlen);
 
-	if (strncmp(base, path->buf, strlen(base)))
+	if (prefixcmp(path->buf, base))
 		strbuf_addbuf(&rel, path);
 	else
 		strbuf_addstr(&rel, path->buf + strlen(base) + 1);