bug#22832: 25.0.91; Keyboard navigation broken on menus

[Óscar Fuentes]

emacs -Q

;; disable menu bar:
M-x menu-bar-mode

Press F10 to show the menu. It is not possible to navigate the popup
menu using the keyboard. This worked fine on

GNU Emacs 25.0.50.29 (x86_64-unknown-linux-gnu, X toolkit) of 2016-01-21
5293d1bdb3e665a565af032a163004c976328cc2



In GNU Emacs 25.0.91.3 (x86_64-unknown-linux-gnu, X toolkit)
 of 2016-02-25 built on qcore
Repository revision: 8be32cf45cd8b39ff6c8dc431b0ac04a0959786d
Windowing system distributor 'The X.Org Foundation', version 11.0.11702000
System Description:     Ubuntu 15.10

Configured using:
 'configure --without-toolkit-scroll-bars --with-x-toolkit=lucid'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY GNUTLS LIBXML2
FREETYPE XFT ZLIB LUCID X11

Important settings:
  value of $LANG: C
  locale-coding-system: nil