your gonna get a lot of ppl going both ways on this subject, but my thinking is that you should always have the clutch out. the subtle torque of the engine even at idle can vastly improve traction through a corner, i would downshift.
I personally don't think you should coast into a corner with the clutch in. You should choose the correct gear and slip the clutch if necessary to ensure you have the right amount of engine revs when exiting the corner. You should be either hard on the acceleration or hard under brakes - no coasting.