Handle Alt+Numpad key sequences in console input and select

{p}select/{p}poll completely ignored Alt+Numpad key sequences in console
input which results in newer readline using pselect to fail handling such
sequences correctly.  See https://cygwin.com/ml/cygwin/2017-01/msg00135.html

During debugging and testing it turned out that while reading console
input, single key presses during an Alt+Numpad sequences where not
ignored, so ultimately a sequence like

  Alt-down Numpad-1 Numpad-2 Numpad-3

whihc is supposed to result in a single character in the input stream
will actually result in 4 chars in the input stream, three control
sequences and the actual character.

Both problems should be fixed by this patch.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_console.cc

@@ -7,6 +7,7 @@ Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
 #include "winsup.h"
+#include <dinput.h>
 #include "miscfuncs.h"
 #include <stdio.h>
 #include <stdlib.h>
@@ -415,6 +416,17 @@ fhandler_console::read (void *pv, size_t& buflen)
 		// left alt -- see http://www.microsoft.com/hwdev/tech/input/Scancode.asp
 		&& input_rec.Event.KeyEvent.wVirtualScanCode == 0x38))
 	    continue;
+	  /* Ignore Alt+Numpad keys.  These are used to enter codepoints not
+	     available in the current keyboard layout.  They are eventually
+	     handled in the key-up case below.  For details see
+	     http://www.fileformat.info/tip/microsoft/enter_unicode.htm */
+	  if (input_rec.Event.KeyEvent.bKeyDown
+	      && wch == 0
+	      && input_rec.Event.KeyEvent.dwControlKeyState == LEFT_ALT_PRESSED
+	      && input_rec.Event.KeyEvent.wVirtualScanCode >= DIK_NUMPAD7
+	      && input_rec.Event.KeyEvent.wVirtualScanCode <= DIK_NUMPAD0
+	      && input_rec.Event.KeyEvent.wVirtualScanCode != DIK_SUBTRACT)
+	    continue;
 
 	  if (control_key_state & SHIFT_PRESSED)
 	    con.nModifiers |= 1;