Re-apply "[serialization] Reject loading a module with the wrong case."

This included a test that failed on case-sensitive filesystems. Test fixed.

(Aside: Why not just have this fail with "no such module"? Why use a different
error? Because even if "import FOO" picks up a module named 'Foo', there may
actually be a module named 'FOO' on the system (in another folder), and we
should be able to find that. Fixing that is tracked by rdar://problem/18691936.)

rdar://problem/15632996 (again)

Swift SVN r22856

lib/Serialization/ModuleFile.cpp

@@ -504,7 +504,8 @@ ModuleFile::ModuleFile(
     case CONTROL_BLOCK_ID: {
       cursor.EnterSubBlock(CONTROL_BLOCK_ID);
 
-      ModuleStatus err = validateControlBlock(cursor, scratch).first;
+      ModuleStatus err;
+      std::tie(err, Name) = validateControlBlock(cursor, scratch);
       if (err != ModuleStatus::Valid) {
         error(err);
         return;
@@ -746,6 +747,11 @@ bool ModuleFile::associateWithFileContext(FileUnit *file, SourceLoc diagLoc) {
   assert(!FileContext && "already associated with an AST module");
   FileContext = file;
 
+  if (file->getParentModule()->Name.str() != Name) {
+    error(ModuleStatus::NameMismatch);
+    return false;
+  }
+
   ASTContext &ctx = getContext();
   bool missingDependency = false;
   for (auto &dependency : Dependencies) {
@@ -1091,8 +1097,7 @@ ModuleFile::collectLinkLibraries(Module::LinkLibraryCallback callback) const {
   for (auto &lib : LinkLibraries)
     callback(lib);
   if (Bits.IsFramework)
-    callback(LinkLibrary(FileContext->getParentModule()->Name.str(),
-                         LibraryKind::Framework));
+    callback(LinkLibrary(Name, LibraryKind::Framework));
 }
 
 void ModuleFile::getTopLevelDecls(SmallVectorImpl<Decl *> &results) {