runtime using BN_CTX_new(). This is done since in OpenSSL 0.9.7e we
can only allocate BN_CTX on the stack by including an internal OpenSSL
header file, and in OpenSSL 0.9.8 BN_CTX is entirely opaque, so having
it on the stack is not possible at all.
This is done as preparation for OpenSSL 0.9.8b import.
Tested on: amd64 i386 ia64
Tested with: src/tools/regression/lib/libmp