client: Be more clear about when one must call wl_display_flush
client: Be more clear about when one must call wl_display_flush

Blocking in general is not what means it is required to flush, but
blocking on input from the wl_display file descriptor.

Signed-off-by: Jonas Ådahl <67dcd8a17e758192e0cbb577ce1d62cc7da6cf49@gmail.com>
Reviewed-by: Bryce Harrington <bdb14cfc1ab8d24e13de84adc40b41ae60c13bd1@osg.samsung.com>

mchalupa/wayland,tulcod/wayland,sir-murray/wayland,tulcod/wayland,sir-murray/wayland,abooij/wayland,tulcod/wayland,sir-murray/wayland,mchalupa/wayland,abooij/wayland,abooij/wayland,mchalupa/wayland