dc(1) bugs

[CK]

http://lists.freebsd.org/pipermail/freebsd-questions/2016-January/269999.html

I posted some dc(1) bugs there for review, and it appears that they are
indeed bugs.  Also cited in a followup, is why dc(1) is a critical tool;
additionally, it should be expected that a modern computer havs a
simple functional calculator for the command-line. Considering dc(1)
predates all other tools demonstrates it's basic value in computing.