xcb/util-keysym: Recognise ISO_Level5-keysyms as modifiers in xcb_is_modifier_key #39177

[Andreas Wettstein]

In August, I submitted a patch for xcb-bug #39177.  It has been
reviewed, but has not been applied.

  http://patchwork.freedesktop.org/patch/6622/

Can someone have look?

Thanks,

Andreas