db-lib unit test change

I re-worked the db-lib unit tests this weekend, just in time for the
Superbowl.  

The idea is to make them easier to understand and modify, although I'm not
sure how successful I was.  It *is* a lot easier to see the SQL now -- and
quicker to test new changes -- at the cost of the code being a little more
opaque because the SQL is no longer interspersed with the dbsqlexec()
calls.  

The other idea is to make it possible to execute the unit test sql using
other, non-FreeTDS (and, yea, even on nonfree) tools, to see if they
behave as expected.  That kind of testing is needed to find ever more
obscure compatibility issues with the vendors' libraries.  

Happy hacking.  

--jkl