Currently the email module maintains a set of "charset" aliases that it maps to codec names before looking up the codec in the codecs module.  Ideally it should instead be able to just look up any 'charset' name, and if it is a valid alias for a codec, the codec module would return the codec with the canonical name.  It is possible (I haven't checked yet) that the email module needs a different canonical  'charset' name for certain codecs, but if so it can do that mapping after getting the canonical codec name from codecs.

To implement this we need to make two simple changes:

1) add any aliases the email module recognizes but the codecs module doesn't to the codecs module.

2) rewrite email.charset so that it does not have an ALIASES table (but may have a smaller 'canonical charset map' table instead).