[PATCH] Implement uuid_version()

Hackers,

    While working on an application, the need arose to be able
efficiently differentiate v4/v5 UUIDs (for use in partial indexes, among
others)

... so please find attached a trivial patch which adds the
functionality. The "uuid_version_bits()" function (from the test suite?)
seems quite a bit hackish, apart from inefficient :(

    I'm not sure whether this actually would justify a version bump for
the OSSP-UUID extension ---a misnomer, BTW, since at least in all the
systems I have access to, the extension is actually linked against
libuuid from e2fsutils, but I digress --- or not, given that it doesn't
change exposed functionality.

    Another matter, which I'd like to propose in a later thread, is
whether it'd be interesting to include the main UUID functionality
directly in core, with the remaining functions in ossp-uuid (just like
it is now, for backwards compatibility): Most current patterns for
distributed/sharded databases are based on using UUIDs for many PKs.

Thanks,

    J.L.