ANTLR3 C++ Target HPUX error

If you try to build the C++ Target in HPUX, somehow the pair in the TokensType::iterator has a different value than the reference... the ANTLR_MARKER becomes const-qualified, and therefore you can't dereference the pair, breaking any instances with TokensType::iterators being dereferenced.

I don't know why this is happening, but I was able to get it to build by const qualifying the UnOrderedMapType and OrderedMapType in antlr3memory.h:

```
template
class UnOrderedMapType : public std::map< KeyType, ValueType, std::less,
AllocatorType > >
{
};

template
class OrderedMapType : public std::map< KeyType, ValueType, std::less,
AllocatorType > >
{
};
```

Here's a bit more thorough discussion:
https://groups.google.com/forum/#!topic/antlr-discussion/3OU9s4mfXgk

Start with antlr3memory.h and the C++ target build on HP-UX. Review the linked ANTLR discussion and inspect how UnOrderedMapType, OrderedMapType, and their iterators instantiate std::map and AllocatorType. Done means the C++ target builds on HP-UX and dereferencing TokensType iterators works without the const-qualification error.

Written by the indexing model from the issue text.