Deliver debug events to programs in debug mode.
Deliver debug events to programs in debug mode.

A previous change to block delivery of UI events accidentally also
blocked debug events.  They should still be delivered.

Fixes #675.

pranjaltale16/codeworld,pranjaltale16/codeworld,alphalambda/codeworld,pranjaltale16/codeworld,google/codeworld,alphalambda/codeworld,google/codeworld,alphalambda/codeworld,google/codeworld