uri: allow leading dots, but explicitly exclude "." and ".."

Dots at the beginning of an URI segment are ok, as long as the special
names "." and ".." are not used.

src/uri.c

@@ -51,7 +51,10 @@ verify_uri_segment(const char *p)
 {
 	const char *q;
 
-	if (*p == 0 || *p == '/' || *p == '.')
+	unsigned dots = 0;
+	while (*p == '.')
+		++p;
+	if (dots <= 2 && (*p == 0 || *p == '/'))
 		return NULL;
 
 	q = strchr(p + 1, '/');