[crossfire] Patch: Fix map display errors for big faces

[Andreas Kirschbaum]

I just added my patches to fix bug #1102991 (Duplicate grapical display
of the same monster):

   
     
     http://sourceforge.net/tracker/index.php?func=detail&aid=1269280&group_id=13833&atid=313833
     
     


I did add the patch to the tracker instead of just committing it because
it is not just a small bugfix but basically a re-write of the display
logic for all three clients. (The display logic is now in
common/mapdata.c and is shared by all clients.)

I'd like to get some feedback before I actually commit it.

Note that mapdata.c still contains lots of assert() statements. They did
help me to ensure the passed coordinates are valid. I'll remove them
before I commit.