Keep better track of when external process threads are running to avoid crashes if the user closes a window at the wrong time.
Ensure a role is selected to reassign objects to before the user can click OK.
Don't allow the user to try to open help pages from Guru Hints that don't have any.
Original patch by Akshay Joshi, modified by moi.
Fix Slony's DDL Script support.

Conflicts:
	CHANGELOG
Initialise variables properly to avoid random syntax errors in reverse engineered SQL.