let-bound namespace-qualified bindings should throw (if not map destructuring)

Seen in a tweet...

The second one should throw like the first one (also see CLJ-1318 where support for map destructuring of namespaced symbols was added).

Approach: Rather than allowing namespaced symbols to be returned from the map destructuring (the pmap fn), convert those symbols before returning them, so that any namespaced symbols encountered in the main cond of pb are an error and can be handled uniformly.

Patch: clj-1778-2-with-tests.patch

Screened by: Alex Miller