Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Sync with OpenBSD.

MFC after: 2 weeks

- Use BN_set_negative() and BN_is_negative() instead of subtracting or
comparing to zero.
- Fix fractional number exponentiation, especially for negative exponents.

Obtained from: OpenBSD

- style(9)

Approved by: delphij (mentor)

Replace GNU bc/dc with BSDL versions ported from OpenBSD. They have a good
compatibility level with the GNU counterparts and have shown to be mature
enough. For now, the GNU versions aren't removed from the tree, just detached
from the build.

Sponsored by: Google Summer of Code 2008
Portbuild run by: erwin
Approved by: delphij