Patch adding UML transitions, trouble with bounding boxes

[Peter Allin <pallists peca dk>]

Hi,

I've just attached a patch file to bug number 144956. The patch should
add UML statechart transitions to the UML sheet. Any comments are very
much welcome! This is my first shot at submitting code to this project,
so please tell me if I've broken any unwritten (or unread ;-) ) rules in
the code or the way I submitted it.

I have some problems calculating the bounding box for the transition. I
have the orthogonal connector and the texts covered, but the arrowhead
on the connector isn't included in my calculations. This results in some
artifacts when dragging the transition.

As far as I can see in some other objects, I'm supposed to use the
extra_spacing member in the OrthConn struct to add the extra space used
by the arrowhead. But I can't figure out how to use it.

Can anyone help me understanding how it should be used?

Best regards,
 Peter Allin