Sets the maximumNumberOfTouches on the panGestureRecognizer to be as man...

Sets the maximumNumberOfTouches on the panGestureRecognizer to be as many touches as the gesture started with for the duration of the gesture.

This fixes a problem where the keyboard jumps around erratically if you start panning down to dismiss with one finger, and then touch the keyboard with a 2nd finger as it is being scrolled off the screen.