Rewrote our local implementation of a Base64 encoder/decoder as specified

Rewrote our local implementation of a Base64 encoder/decoder as specified
in RFC 2045 section 6.8.   In the past, someone tried to make this "elegant"
and in the process they made it broken when certain conditions exist.  If
you are reading this and it isn't broken, don't try to improve it.  It works
and I don't want to fix it again.  I don't care how many nanoseconds you think
you can shave off the execution time.  Don't fucking touch it.