MFC r307521: libmd: introduce functions that operate on fd instead of filename

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Unbreak build following rev. 282726

(Makefile.inc1): add dependency of xinstall on libmd to
avoid failure of parallel bootstrap.

(lib/libmd/*.h): do not redefine symbols if already
defined as macros (libcrypt uses the same sources internally,
redefining symbols with a prefix of its own).

Fixes build failures caused by previous change to libmd.

Reported by: ian
Pointy hat to: thomas

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
Differential Revision: D2216
Reviewed by: roberto, delphij
MFC after: 2 weeks

Fix an 11 year old mistake: Let the hash functions take a void* instead
of unsigned char* argument.

Add a new entrypoint to the hashes in libmd:
char *
FooFileChunk(const char *filename, char *buf, off_t offset, off_t length)
Which only hashes part of a file.
Implement FooFile() in terms of this function.

Submitted by: roam

$Id$ -> $FreeBSD$

Add Eric Young's RIPEMD160 implementation as well, in case SHA-1
should prove weak. Also fix a few problems with the SHA-1 build.

Fix bug in MDx test suite.
Add Eric Young's SHA-[01] implementations.