Improve support for script variants

[friedelwolff]

Currently Amagama does not correctly support variants like 'sr@latin', and simply imports it with 'sr'. This produces mixed results for someone querying either 'sr' or 'sr@latin'.

Maybe we should just not simplify @ modifiers during code normalisation and matching, although I'm not sure that it is necessarily completely safe.

[dwaynebailey]

This sounds a bit like what I've wanted for ages. The ability to map proper code to some random code. E.g. Mozilla uses hi-IN when not needed. Some way to override or map this in the correct place so that the version control can use what it wants, Pootle uses the correct thing and asks Amagama correctly. Thus Amagama stores the correct code and the import scripts to any mapping changes.