compositor: round off fractions

compositor: round off fractions

Round off fractions from non-transformed surface position coordinates.

Transformed surface moved by a client may have non-integer position
coordinates. That is required to prevent drifting on continuous
resizing.

We can round the position to integers when the surface is not (anymore)
transformed.

This change may fix a rounding inconsistency in the opaque region setup,
where the rectangle is initialised from the coordinates without explicit
rounding operation.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>