swift234

Add a 'current module' parameter to lookupVisibleDecls() so that it can do what
is documented: look up members of a type that are visible from a specific
module.  It does not matter much now, but when we have access control, it will.

Before this change, lookupVisibleDecls() tried to guess the *defining* module
of the type, and gave up if it could not.  It forced us to duplicate some
lookup logic for some types (archetypes and protocol compositions).  Also add a
test that lookup finds members of archetype's superclass, which the original
(duplicated) code did not handle.


Swift SVN r6363