[useful for SoC students] IDs of warning and errors

[Juan Pablo Carbajal]

Hi all,

When raising errors and warnings try to use the ids that are defined
in the functions
warning_ids
error_ids

If you really need a new id (please, first read the ones already
there!), please add it to those functions as well.

If you see other ids used in core that are not given by the functions
mentioned above, please, report or submit patch.

Thanks

Cheers,