Qt key handling

Fix the popup versions of qt_yn_function() to handle control
characters by using the same key press event decoding routine
and menus and extended commands.  Moves 'keyValue()' to
qt_key.cpp and its declaration to qt_key.h, requring several
files to start using #include "qt_key.h".

'make depend' update to follow.

win/Qt/qt_key.h

@@ -9,6 +9,9 @@
 
 namespace nethack_qt_ {
 
+// not part of any class; used in qt_menu.cpp, qt_xcmd.cpp, qt_yndlg.cpp
+extern uchar keyValue(QKeyEvent *key_event);
+
 class NetHackQtKeyBuffer {
 public:
 	NetHackQtKeyBuffer();