GDK W32: Handle drivers that do not send WT_CSRCHANGE after WT_PROXIMITY

Some drivers don't do that (not sure whether that is the correct behaviour
or not). Remember each WT_PROXIMITY with LOWORD(lParam) != 0 that we get,
then look for a WT_CSRCHANGE. If WT_CSRCHANGE doesn't come, but a WT_PACKET
does, assume that this device is the one that sent WT_PROXIMITY.

Also include fallback code to ensure that WT_PACKETs for an enabled device
disable the system pointer, because WT_PROXIMITY handler might have
enabled it by mistake, since it's not possible to know which device left
the proximity (it might have been a disabled device).

https://bugzilla.gnome.org/show_bug.cgi?id=778328

gdk/win32/gdkglobals-win32.c

@@ -35,7 +35,7 @@ HDC		  _gdk_display_hdc;
 HINSTANCE	  _gdk_dll_hinstance;
 HINSTANCE	  _gdk_app_hmodule;
 
-gboolean	  _gdk_input_ignore_core;
+gint		  _gdk_input_ignore_core;
 
 HKL		  _gdk_input_locale;
 gboolean	  _gdk_input_locale_is_ime;