defer() - execute function after current function ends


void defer(function f)


Call function pointer *f when current function ends (even if it 
was due to a runtime error).
For example: 

void create()
  defer( (: enable_commands :) );

The effect the defer() function has is it will cause the 
enable_commands() efun to be called after the execution of the
create() function ends.  The argument passed to defer() can be
any function type.