Fixing a subtle error with deleting tiles and undo.

Undoing and the subsequent deleting of tiles rendered the stored mves
invalid, pointing to now non-existing tiles. Fixed by not deleting tiles
any more; instead, we now set a "conected" flag.
Fixing some meory leaks.
Removed some compiler warnings.

Also worked a bit on the imlpementation of the evaluation function.
Towards a working evaluation function.

Implemented some more parts of the evaluation function. Fixed some bugs
on the way.
Finished the evaluation function.

Fixed some more bugs on the way...