Most parsing errors are reported during parsing itself but sometimes some extra conditions must be checked. One problem with this is that these extra conditions are not met because they are the consequence of a primary error which has already been reported. In this case, it this not desirable to emit a new error message. To help with this, add a small function which will emit an error message followed by the current token but only if the current token does not originated from a previous parsing error. Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>