ilo: construct SCISSOR_RECT in set_scissor_states()

ilo: construct SCISSOR_RECT in set_scissor_states()

This allows us to memcpy() the state in draw_vbo().  Add ilo_init_states() and
ilo_cleanup_states() that are called when contexts are created and destroyed
respectively, and properly set the initial scissor state in ilo_init_states().