Field and message with same name generate invalid code

[swankjesse]

If we have a message that’s unwisely named not-to-pattern, say, taco and a field of that type with the same name, optional taco taco = 1 then the generated code is malformed because Javac cannot differentiate between the field and class name.

Solutions for fixing this are awkward. Do we allocate a different field name? Or always fully-qualify the class?

[mellster2012]

Seems related to #299 which was fixed by #1252.