Choose one or several files, even from multiple directories. Once all the files are shown in the grid you can drag and drop them to reorder. (for example you probably want jQuery to be before any jQuery plugins). Finally you will click Ok. Depending on your clientside settings it with either replace the current open file, copy it to the clipboard, or prompt and ask what to do.
So if you don't already use Gedit or the Clientside plugin I suggest giving it a shot. It can be configured to be very similar to textmate, or make it your own animal! Enjoy!