swift234

REPL: Hook up completions to name lookup.

Implement a 'lookupVisibleDecls' API similar to Clang's that replicates the UnqualifiedLookup logic for walking through a given scope looking for decls. Use it to populate the completion list in the repl.

Still to be done: Clang module lookup via Clang's lookupVisibleDecls, and context deduction from dotted path expressions.

Swift SVN r4056