sys.build_stlist() builds a list of the internal 4C state stack
for ONE program into a file using the sys.t_stlist file definition.
This file can then be read to display the state stack.
Bugs/Features/Comments:
If more than one program is active with the same asprog name,
only the most recently active one is used by sys.build_stlist().
Since this is meant for internal use,
the file definition may change when needed.