Also try to add final to non-public members of public classes.

Teaches TryAddFinal to descend into public and objc classes. Only
tries to add final if we're either whole compilation mode, or we're
processing the primary source buffer.

Updates test cases. Includes workarounds for <rdar://problem/17860781>
and <rdar://problem/17862348>.

Swift SVN r20790

lib/Frontend/Frontend.cpp

@@ -391,7 +391,8 @@ void CompilerInstance::performSema() {
                           Invocation.getCodeCompletionFactory());
   }
 
-  performWholeModuleChecks(MainModule, PrimaryBufferID == NO_SUCH_BUFFER);
+  performWholeModuleChecks(MainModule, PrimarySourceFile,
+                           PrimaryBufferID == NO_SUCH_BUFFER);
 }
 
 void CompilerInstance::performParseOnly() {