Another fix for handling of file names on Windows 9X.

Another fix for handling of file names on Windows 9X.

 src/w32.c (pMultiByteToWideChar, pWideCharToMultiByte): New
 variables: pointers through which to call the respective APIs.
 (filename_to_utf16, filename_from_utf16, filename_to_ansi)
 (filename_from_ansi, sys_link, check_windows_init_file): Call
 MultiByteToWideChar and WideCharToMultiByte through pointers.
 This is required on Windows 9X, where we dynamically load
 UNICOWS.DLL which has their non-stub implementations.
 (maybe_load_unicows_dll): Assign addresses to these 2 function
 pointers after loading UNICOWS.DLL.
 src/w32fns.c (Fx_file_dialog, Fw32_shell_execute) [!CYGWIN]: Call
 MultiByteToWideChar and WideCharToMultiByte through function
 pointers.
 src/w32.h (pMultiByteToWideChar, pWideCharToMultiByte): New
 declarations.