Updated equation_of_time.c, solar_declination.c, and ephemera_common.h, for a better fit to USNO data. 

I had been using data from both USNO and NOAA, before discovering that they do not agree on some important data points. 

This update resolves the issues I have been having with these to functions.

git-svn-id: http://svn.savannah.nongnu.org/svn/avr-libc/trunk@2345 1084037a-409f-4a99-8160-1a4b3577d4c1