[antlr-interest] syntactic predicates and exceptions

[Ric Klaren]

With antlr3 it's just a matter of putting in different codegeneration
templates to tweak the code generated, so accomodating either option
should not be a big problem. Some extra suppor (or changes to) classes
in the runtime might also be required.

For C codegen in v3 using ifs was easily implemented in the templates only.

Tweaking the generated code will be very easy in v3 (I hope we'll
figure out a good mechanism to specify overrides)

Cheers,

Ric