WhereMany doesn't work with custom attributes about minq

[theodox]

3 options here:

1. second class lilke item that always uses Where() instead of WhereMany()
2. annotate the where() call itself to pick the right specialization
3. Try-except in the query. Probably slow, but least work for user.

[theodox]

OK, fix is is for now - this uses 3 options:

1. the existing item. which defaults to (slow) Where() queries. Left in for compatibility
2. a new native which uses WhereMany.
3. a new custom, which uses Where