Convert openssl(1) to using BN_GENCB on the heap

Convert openssl(1) to using BN_GENCB on the heap

This is three times the same thing while genrsa needs some extra steps
to deal with opaque BIGNUMs. We can also garbage collect some Win 3.1
contortions and use the conversion routines directly instead of doing
them manually.

ok jsing