compositor: warn about insane repaint delay
compositor: warn about insane repaint delay

Make the sanity check more explicit and log a warning if it happens.

Small negative values are ok because it just means the compositor is
lagging behind, or more likely the user specified a too long repaint
window.

Signed-off-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>
Reviewed-By: Derek Foreman <2f97e0f0bc172406aab8ccd42dab54c95bab8759@osg.samsung.com>
Reviewed-by: Bryce Harrington <dd437fc32dcda8cbb48d47baa844ad777493d02b@samsung.com>

giucam/weston,Fantu/compositor-spice,krezovic/weston,eyolfson/weston,sir-murray/weston,mchalupa/weston,jonnylamb/weston,Fantu/compositor-spice,jonnylamb/weston,krezovic/weston,giucam/weston,Gnurou/weston,mchalupa/weston,sir-murray/weston,kwm81/weston,Gnurou/weston,Tarnyko/weston-xdg_surface_present,xorgy/weston,xorgy/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,udoprog/weston,udoprog/weston,kwm81/weston,eyolfson/weston