Replace Undefine_Type comparison with __is_initialized test

This will take some time probably. New slang version effectively
treats all undefined variables as errors. Yes, this renders the
Undefine_Type absolutely useless... So, variables can be declared
and not initialized, but as soon as the are used things will go
south. The proper way to test this is

__is_initialized(&potentiall_undefined_variable);

Yes, it takes a pointer. Fix here for optimal binning.

Oh, and, yes, this is a run time error. That means they will only
show up once in use...