Remove duplicated names from namedef.h

- Added an assertion in FName::NameManager::InitBuckets() that makes these
  errors easier to spot in the future.

src/name.cpp

@@ -182,6 +182,7 @@ void FName::NameManager::InitBuckets ()
 	// Register built-in names. 'None' must be name 0.
 	for (size_t i = 0; i < countof(PredefinedNames); ++i)
 	{
+		assert(NULL == FindName(PredefinedNames[i], true) && "Predefined name already inserted");
 		FindName (PredefinedNames[i], false);
 	}
 }