Mac OS X defines uint_fast32_t to unsigned int, causing ambiguous
overloads between RAIIdmem::operator[](std::size_t) and
RAIIdmem::operator[](int). Adding a disambiguating overload for OS X
breaks Windows. Remove operator pointer and operator[]. Rely on the
inherited operator[] for indexing. Require users to call ->get() to
convert to a simple pointer.
First btb ambiguity reported: https://github.com/dxx-rebirth/dxx-rebirth/pull/34
Second btb ambiguity reported: https://github.com/dxx-rebirth/dxx-rebirth/pull/43
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