Paranoia: in ASN1_mbstring_ncopy(), check for len < 0 instead of len == -1,
in order to catch all negative sizes.
Remove useless comments in DES_is_weak_key(). Do we really care that this
function was found broken in 1993, and later on in 1997?
Use O_NONBLOCK over FIONBIO.

Prefer this because it is the POSIX standard and has consistent behavior
across platforms.

Use BIO_socket_nbio consistently across the tree.

from Jonas 'Sortie' Termansen, ok deraadt@
The return value on success of fcntl(F_SETFL) is not actually specified,
only that it returns -1 on failure.

pointed out by guenther@