Pie Menu Arrow Navigation

Allow the use of arrow keys to navigate through the pie menus.

for example: Press Z to changing world shading. the right most shading option is highlighted. press up or left to move counterclockwise. press down or right to move clockwise. buttons change depending on whats highlighted. Enter selects the highlighted option.

This would be useful when working on a laptop without a mouse. I know they are numbered but I bet i am not alone in instinctively trying to use the arrow keys instead.