[developers] Trigger rules with specialization

[Ann Copestake]

I think of the trigger rules as a hack.  I think there should be a
better solution, but I don't know what it is!  (I supervised a short
master's project on automatically learning the rules several years
ago.  It showed some promise with the ERG, but certainly didn't
provide a full solution - I can forward the thesis to anyone
interested.)  Anyway, if there's an easy-to-implement extension that
works better than the current version, then great - I/we can worry
about whether it can be made to work in the LKB generator once you've
got it debugged ...  

Cheers,

Ann