Bring back an important assertion

Author: DougGregor

lib/AST/DeclContext.cpp

@@ -882,7 +882,7 @@ void IterableDeclContext::addMember(Decl *member, Decl *hint, bool insertAtHead)
 
 void IterableDeclContext::addMemberSilently(Decl *member, Decl *hint,
                                             bool insertAtHead) const {
-//  assert(!isa<AccessorDecl>(member) && "Accessors should not be added here");
+  assert(!isa<AccessorDecl>(member) && "Accessors should not be added here");
   assert(!member->NextDecl && "Already added to a container");
 
 #ifndef NDEBUG