two test cases for OPTIONAL { { ... FILTER ( ... ) } } construct

As promised in the teleconference.

See the two tests

optional-filter/manifest#dawg-optional-filter-005-simplified

and

optional-filter/manifest#dawg-optional-filter-005-not-simplified

...which differ only in the results.

I'm going to solicit implementation behavior and desire on this as 
discussed in the teleconference.

FWIW, Glitter+Anzo passes the not-simplified test and fails the 
simplified test -- I need to dig a bit but I think this is because I 
attach the FILTERs to the OPTIONAL when I'm parsing, and even though I 
do then simplify the group-containing-a-single-group construct, I don't 
re-attach the FILTER at that point. I'd be content with either behavior, 
especially if one is clearly preferred by implementations.

Lee