Currently Xephyr doesn't inherit host X server's keymap, which
may lead to keymap mismatches when using a non-US keyboard in a
window inside Xephyr. This patch makes Xephyr change its keymap
to match host X server's one (unless XKB support is disabled),
using xcb-xkb to retrieve the needed XKB controls.
This implementation is analogous to Xnest one at commit 83fef4235.
Supersedes: https://patchwork.freedesktop.org/patch/67504
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Laércio de Sousa <laerciosousa@sme-mogidascruzes.sp.gov.br>