rpn 5.16.alpha3 - more bug fixes

Several bug fixes, including ones not having directly to do with unit
conversion

I finally decided to handle 'light-second', et al, with special
exceptions rather than mess around with the aliases, etc.  The situation
was just too dumb otherwise.   The only other alternative is to call a
'light-second' a 'speed_of_light-second'.

Also updated the copyright date to 2014.