Use explicit CreateFileA function to create a dump file in Windows

  1. The dump file name is a std::string therefore `CreateFileA()` function should be used in order to compile in a Unicode project.

  2. Use boost::hash_map if no PION_HASH_MAP and PION_HASH_MULTIMAP has been configured

  3.  Define is_iless and ihash_windows for Visual C++ only if stdext::hash_multimap was configured as a ihash_multimap implementation
There are 3 commits in this pull request, each of these commits are described in my first comment.