Legal fix

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Alternate colorbufs, not depth attachments

This is a much easier division for the current API to handle smoothly.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Let targets clear buffers before being hit

This prevents us from having to manipulate colorbufs manually at all during
drawing.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>