Remove the per dungeon level door limit

Number of doors in a room-and-corridor style level was fixed
at 120; now the doors-array is dynamically allocated when needed.

Breaks saves and bones.

doc/fixes3-7-0.txt

@@ -2107,4 +2107,5 @@ for Planes of Water and Air, save the air bubbles and clouds with the level
 switch to a flags arg on newcham() in place of the pair of boolean args
 replace some old 'time_t' hackery in system.h and hacklib.c with something
 	less obtrusive in unixconf.h
+remove the per dungeon level door limit