Clean up pin configuration for peripheral code. Here's the best practice

Clean up pin configuration for peripheral code.  Here's the best practice
for platforms.  MotePlatformC defines pins, using also the new PxREN feature,
such that the peripheral pins are inputs with pull up/down's, or outputs, as
required to meet the electrical characteristics when the peripheral is not on.
In the peripheral's implementation of ResourceConfigure, it sets module
function on configure() and sets back to IO funtion on unconfigure(), but
only if the pin was set to IO mode when configure() was called.  This latter
condition allows a MotePlatformC to set peripheral mode on for pins that will
always be used for peripheral function, and the modes won't switch around.