If the Clang declrations are *types*, canonical declaration in Swift is
imported for newest version of Swift. In interface generation, if the
declaration is versioned and it's imported as a member in either or both
version of Swift, we have to take compatibility typealias into account.
* Fixed 'ClangModuleUnit::getTopLevelDecls' to take isCompatibilityAlias() into account
* Fixed bugs in ClangImporter where member-to-member versioned types aren't properly imported.
* Fixed 'SwiftDeclConverter::importFullName' to check equality of getEffectiveContext()
* Fixed 'importer::addEntryToLookupTable' to check equality of getEffectiveContext()
(moved 'ClangImporter::Implementation::forEachDistinctName' to 'NameImporter')
