Make memory.cxx serve its purpose

The purpose of memory.cxx is to #define _ABC_MEMORY_HXX_IMPL and pull in
abc/memory.hxx in order to define functions otherwise inlined by that
header. This was lost at some point, when abc/core.hxx stopped including
other abc headers.
Suppress more MSC compiler warnings
Fix MSC compiler error affecting Win32 (but not Win64)