Implement wrapper macros for mutex manipulations, support W32 native mutex, require at least WinXP headers on W32

git-svn-id: https://gnunet.org/svn/libmicrohttpd@32865 140774ce-b5e7-0310-ab8b-a85725594a96
Use MHD mutex macros

git-svn-id: https://gnunet.org/svn/libmicrohttpd@32866 140774ce-b5e7-0310-ab8b-a85725594a96
ChangeLog update

git-svn-id: https://gnunet.org/svn/libmicrohttpd@32867 140774ce-b5e7-0310-ab8b-a85725594a96