Extract predicate functions from the stream tagged-* fns

Lets the tagged tests be used in where test expressions
without duplicating logic.

Also removes a branch from the stream tagged-* functions
by coercing single tags into a collection before calling
the predicate.
Test collections of tags in where exprs

Lets tagged, tagged-all & tagged-any be used
with multiple tags in the test expression of
a where clause.
Merge pull request #228 from samn/where-tagged-coll

Support for multiple tags in where test expressions