removed rpn list dependency from error items

the program model was modified to set the error item immediately after
detecting a translator error, otherwise the error item is empty; this
error item is then passed to updateError() instead of using the rpn list
pointer contained in the line info item (which will eventually be
removed)

a none error type was added to the error item to indicate the error item
does not contain an error along with an is empty access function; the
translator and encoder types were changed to the input and code error
types; and a default constructor was added to set an empty error item

to allow errors to be created from encoder errors (though there are none
now), the rpn list dependency (with translator errors) was removed from
the error item class (the error column, length and message is passed to
the constructor instead of an rpn list pointer)