Generated files from deleted grammars persist even with --clean

[krame505]

Currently, when generating translation we only delete existing generated files from the directories corresponding to grammars that are being built; however files from grammars that no longer exist can persist and be seen by ant, causing java compilation problems. --clean currently works by treating every interface file as out of date, and just re-translates every grammar dependency, so this still happens even with a clean build.

I suppose we could have --clean just blow away the contents of the whole generated directory. This would also delete existing generated parsers, but that seems like reasonable behavior for a clean build. (Currently I think parsers don't get regenerated with --clean if the copper spec doesn't change? Which might cause unexpected behavior when experimenting with changes to Copper.)

[krame505]

I guess just nuking the generated directory with --clean doesn't really fully solve the problem, since we would then have another instance of "build fails without --clean". We also don't want to delete generated files from grammars that just aren't triggered in the current build.

Maybe we just need to be more explicit about which source directories are included in ant build file that we generate?