Introduce EVP_MD_CTX_ctrl(), to allow for fine control of a given digest.
This functionality was already available (and optional), and used in the
bowels of the ASN.1 code. This exposes it as a public interface, which will
be used by the upcoming GOST code.
Crank libcrypto minor version.

From Dmitry Eremin-Solenikov.
GOST crypto algorithms (well, most of them), ported from the removed GOST
engine to regular EVP citizens, contributed by Dmitry Eremin-Solenikov;
libcrypto bits only for now.

This is a verbatim import of Dmitry's work, and does not compile in this
state; the forthcoming commits will address these issues.

None of the GOST code is enabled in libcrypto yet, for it still gets
compiled with OPENSSL_NO_GOST defined. However, the public header gost.h
will be installed.