special-case more accurate answer for exp(1.0)
more accurate comment for the x==1.0 hack
new polynomials for erff, by Steve Kargl

these are both faster and more accurate

see http://svnweb.freebsd.org/base/head/lib/msun/src/s_erff.c?view=log
updates to s_round.c from FreeBSD
Enable stack protection in all .S files

Hardware stack protection is required by most distributions.
See https://wiki.gentoo.org/wiki/Project:Hardened/GNU_stack_quickstart