replace_program - replaces the program in this_object()

void replace_program( string str );

replace_program() replaces the program in this_object() with that of an 
object it inherits.  The string argument is the filename of the object 
whose program is to be used.  Once the replacement takes place, the current 
object effectively becomes a clone of that other object, but with its 
current filename and global variable values. The program is not actually 
replaced until the current execution is completed.

Note that one effect of this is that all functions defined in the object
no longer exist, being replaced by the functions in the inherited program,
so this routine should not be called if one of those functions might be
called later (and in particular, create() needs to exist if you intend to
clone from the object).

 Tim Hollebeek  Beek@ZorkMUD, Lima Bean, IdeaExchange, and elsewhere
