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_xcmd.cpp

@@ -90,6 +90,7 @@ extern "C" {
 #include "qt_post.h"
 #include "qt_xcmd.h"
 #include "qt_xcmd.moc"
+#include "qt_key.h" // for keyValue()
 #include "qt_bind.h"
 #include "qt_set.h"
 #include "qt_str.h"