Fix compilation of menus/volumes_menu.c on Windows

One include was missing after latest changes in header files.
Remove useless Windows define in commands.c

It caused compilation error, because of macro being redefined (firstly
defined in implicitly included header).
Better Windows includes in win_helper.c

 - Don't check for _WIN32, it's kinda stupid for Windows-only code.
 - Define WINVER only when it's undefined.
 - Check WINVER value if it's defined.
Merge branch 'fix-win-include-after-updates'