If there is a type context, hide literal suggesetions that don't match
it, unless they are keywords and we have filtered to their names.
Incidentally fix an output buffering issue when combining filtering with
the -raw flag in complete-test.
Part of rdar://problem/23865118
This makes it more clear what the response string contains, plus you can copy the
printed request directly for passing to sourcekitd_request_create_from_yaml.
The code goes into its own sub-tree under 'tools' but tests go under 'test',
so that running 'check-swift' will also run all the SourceKit tests.
SourceKit is disabled on non-darwin platforms.
