pgsql: Improve regression tests for uuid-ossp.

Improve regression tests for uuid-ossp.

On reflection, the timestamp-advances test might fail if we're unlucky
enough for the time_mid field to change between two calls, since uuid_cmp
is just bytewise comparison and the field ordering has more significant
fields later. Build some field extraction functions so we can do a more
honest test of that. Also check that the version and reserved fields
contain what they should.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/c0f27628d2fb53e8e5d190da2132739a2bb2f500

Modified Files
--------------
contrib/uuid-ossp/expected/uuid_ossp.out | 60 +++++++++++++++++++++++-------
contrib/uuid-ossp/sql/uuid_ossp.sql | 49 ++++++++++++++++++++----
2 files changed, 88 insertions(+), 21 deletions(-)