[jaiguru] first working line-jumps implementation.

Hi,

This is a first working line-jump implementation. There's still some code cleanup & documentation to do, and preference pane is not updated.

Could you please test it to see if it really works (it seems so, but I'd like more tests) :-)

The only case where it doesn't create line jumps is when a connection cross itself.

Regards

Jaiguru