For now provide prototypes instead of including the
non-standard normalisation.h which is only available in the
"Internationalized Domain Names Mitigation APIs" download.
changed windows.h include to system header;
changed obsolete 2nd check for str_w to str_utf8 in order to catch
malloc() failure and avoid a free(NULL);
changed calls to GetLastError() to void to kill unsused var compiler
warnings;
moved one call to GetLastError() into else case so that its only
called when WideCharToMultiByte() really fails.
