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.

src/lib/libcrypto/crypto/shlib_version

@@ -1,2 +1,2 @@
 major=30
-minor=1
+minor=2