[patch] draggable having helper as a function

[patch] draggable having helper as a function

Posting here because bug tracker is down. :)
Currently if you set the draggable helper option to a function it
causes an exception because 'e' is not defined in createHelper.
Attached patch contains fix and tests.
Also, thanks for opening up the dev mailing list, its great to see
what is going on behind the scenes