Handle Ctrl+AltGr on Windows

Improve AltGr detection even further on Windows so we can detect the
case when Ctrl and AltGr are pressed together.
diff --git a/doc/keyboard-test.txt b/doc/keyboard-test.txt
index 6375a9e..d66e853 100644
--- a/doc/keyboard-test.txt
+++ b/doc/keyboard-test.txt
@@ -66,7 +66,8 @@
 
   - CapsLock, NumLock
   - Shift, Ctrl
-  - Alt, AltGr, Super [Win, X11] (FIXME: Ctrl+AltGr broken on Win)
+  - Alt, AltGr, Super [Win, X11]
+  - Ctrl+AltGr [Win]
   - Meta [X11]
   - Left/right identification (FIXME: broken for Shift on Win)
   - CmdL => AltL, CmdR => SuperL, AltL => ModeSwitch, AltR => Level3Shift [OS X]
@@ -75,7 +76,6 @@
   - CapsLock, Shift and AltGr affect symbol lookup
   - Ctrl does not affect symbol lookup
   - Ctrl+Alt+<ANY> sends the same symbol as <ANY>
-  - Ctrl+AltGr+<ANY> sends the same symbol as AltGr+<ANY> (FIXME: broken on Win)
   - "Shift press, A press, Shift release, A release" should not send "a release"
 
 - Numpad: