When tray icon gets destroyed, space it was occupying would not be cleaned, yielding wholes inside taskbar. Fixing by explicitly hiding and deleting FLTK window which holded application tray window.
By default, pekwm will reorder window list on input focus (probably to optimize things) and this would also reorder buttons inside taskbar. Also, on new window list, all panel buttons would be recreated again, causing many allocations and deallocations. Now, window list received from wm is compared agains internal window storage for diffs.
Fixing this issue made removal some old edewm specific code and made panel nicely working under sawfish ;)
This change should make base applet code easier to modify without modifying applets itself. This is also
a starting point for implementation of better routing netwm messages to applets without adding specific listener
to each applet.
