Support 'clone' Sublime 1.4 ability

It seems that you can do it like this:
* Click on e.g. "Horizontal Double Pane Layout".
* Go into one pane and load a file.
* Go into the other pane and load that file again using "Goto File".

But there seems to be a on_clone event in sublime_plugin.py. So I hope that we can do this a little bit easier in the future.

! thanks!

Suresh, this has been implemented on build 2036 with the File/Clone command. Unfortunately I can't take full advantage of it beacuse in (at least my) Linux OS the Layout options aren't working yet.