Qt: ^V on OSX

I can't take credit for this and still have no idea why it is
needed, but it fixes use of ^V as a command and as input to
to the regular version of yn_function().  In particular, '&'
command reports it as ^V.  Unfortunately when 'popup_dialog' is
set, no control characters seem to be accepted by the part of
NetHackQtYnDialog(Exec+KeyPressEvent) responsible for arbitrary
input.

It also causes getlin() to terminate but I can't think of any
situation where ^V would be considered to be valid input for
getlin() so won't worry about that.

I put it in as '#if MACOSX' because I don't know whether any
other Qt platforms need it.

win/Qt/Qt-issues.txt

@@ -40,10 +40,6 @@ On OSX, command+Q while a menu (which has its own key event handler)
 is popped up gets ignored.  It should at least close the popup like
 ESC and maybe also initiate quitting.
 
-On the map, ^V is a dead key (at least on OSX; all other ASCII control
-characters from ^A through ^U, ^W through ^Z, and ^[, ^\, ^], ^^, ^_
-work; no attempt to have ^@ generate NUL has been made).
-
 Map column #0, which the core reserves for its own purposes and isn't
 intended to be displayed, is displayed (as blank terrain).