fixed twi implode() calls (wrong parameter order)

implode() wants to have $glue first, then $pieces: http://php.net/implode

The note on that page says:
implode() can, for historical reasons, accept its parameters in either order. For consistency with explode(), however, it may be less confusing to use the documented order of arguments.

 So it was not really a bug, only a bit ugly :-)

src/transports/imap/imap_transport.php

@@ -1089,7 +1089,7 @@ public function fetchSizes( $messages )
         }
 
         $sizes = array();
-        $ids = implode( $messages, ',' );
+        $ids = implode( ',', $messages );
 
         $tag = $this->getNextTag();
         $this->connection->sendData( "{$tag} {$uid}FETCH {$ids} (RFC822.SIZE)" );
@@ -2035,7 +2035,7 @@ public function fetchFlags( $messages )
         }
 
         $flags = array();
-        $ids = implode( $messages, ',' );
+        $ids = implode( ',', $messages );
 
         $tag = $this->getNextTag();
         $this->connection->sendData( "{$tag} {$uid}FETCH {$ids} (FLAGS)" );