+ 29.8.2001 Goetz
+ Added routine to free irgraphs.
+
+ 17.7.2001 Goetz
+ Improved add routines to sub, supertype in type.c
+
+ 12.r7.2001 Goetz
+ Added implementation of overwrites stuff.
+
+ 11.7.2001 Goetz
+ Implemented stuff to change the type graph. See
+ typegmod.h and tpop.h for basic documentation of the change.
+ There now exists a type of kind type_id. If this appears
+ externally this is a bug.
+
9.7.2001 Goetz
Added some new access routines to types.
List of overwritten fields for entities.