C++ fixes for building with Ice >= 3.4

Fix the various *Ptr typedefs to use IceInternal::Handle rather than IceUtil::Handle, as seen in the code generated by slice2cpp and recommended as a workaround by zeroc.

Note that the second patch (65ee8d7) has some fairly dodgy escaping in it, and I don't like it.  However, this is the only combination of escaped and unescaped leading '#'s which would build; none failed to build the headers, all failed to compile due to retaining some escapes in the output header.  This is the combination which both generates and compiles, but the reason for this odd behaviour is not clear.