minor fixes as per Tridge's suggestions

- changed 'unsigned' to 'uint8_t'
- moved rally_location_to_location from static function to private
member
- removed _rally_wp_size member variable (only used in ctor)
- added a check that the rally point size passed in matches
sizeof(RallyLocation), to help catch any drift over
time/compiler/hardware/etc
Merge commit '99f714a0df1c5b6207e8e81e20c5f06d60cc950a' into AP_Rally_Copter
oops - removed some commented-out debug statements