Added 'U'/'u' for number of points in addition to 'n'.  'U' looks like an upside down 'N'.

See:
http://3dprintboard.com/showthread.php?6165-Marlin-firmware-fork-for-Mak
erFarm-i3v-w-auto-bed-level-amp-Roxy-s-enhancements&p=28278&viewfull=1#p
ost28278