MFC r282726: Ensure libmd symbols do not clash with libcrypto

MFC r282726: Ensure libmd symbols do not clash with libcrypto

Add a prefix to all symbols in libmd to avoid incompatibilites
with same-named, but not binary compatible, symbols from libcrypto.

Also introduce Weak aliases to avoid the need to rebuild dependent
binaries and a major version bump.

PR:		199119

git-svn-id: svn://svn.freebsd.org/base/stable/10@314144 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f