Reinstate "canonicalization" of path names for file URIs

This reverts commit 4f0aaa166e245aba08c574c0b4b8ae32bbc535dc
and insert check for the "//" -> "/" change only to occur for
file:// URIs. This fixes the recent reports on broken handling
of relative file URIs starting with "..".

src/protocol/uri.c

@@ -766,6 +766,11 @@ normalize_uri(struct uri *uri, unsigned char *uristring)
 				continue;
 			}
 
+		} else if (is_uri_dir_sep(uri, src[1]) &&
+			   uri->protocol == PROTOCOL_FILE) {
+			/* // - ignore first '/'. */
+			src += 1;
+			continue;
 		}
 
 		/* We don't want to access memory past the NUL char. */