swift234

Validate import kind, e.g. "import var swift.max" now errors, with fix-it.

Again, the import kind rules are:
 - 'import KIND' can import any decl whose introducer is KIND.
 - 'import typealias' can also import a struct, class, or union.
 - Conversely, 'import KIND' can import a typealias for a decl whose
   introducer is KIND.
 - Only functions can be overloaded; anything else counts as an ambiguous
   import and is an error.
 - If an import statement only imports a single decl, but the user got the
   kind wrong, we can issue a fix-it for the kind.

We don't have source locations or synthetic source for declarations yet,
so there are no notes about what's /causing/ the ambiguities. Tracked by
<rdar://problem/14650883>

Swift SVN r6917