corrected token memory leaks caused by error conditions

a new sub-code was implemented to indicate when a token with an error
has not been used in the RPN output list (which are deleted when the
output list is cleared when an error is detected) so that the token can
be deleted; this sub-code is used in getOperand() with a command or
operator token, and when the terminating token is not an EOL token (the
check for which needed to be prefixed for whether the token has a table
entry since any token may have terminated the expression)