dblib unit tests

I began to modify our unit tests to work with Microsoft's db-lib.  Some of
our tests "pass" FreeTDS but fail with Microsoft's.  Some can't be
compiled.  

In the case of t0013, if failed because the test was wrong.  FreeTDS
permits dbwritetext() after dbresults() returns NO_MORE_ROWS, and t0013
took advantage of that.  Microsoft's library complained of an invalid
textptr.  Docs don't say, but the examples all call dbwritetext() -- with
another DBPROCESS -- after dbresults() returns REG_ROW.  

After modifying t0013 to work with Microsoft's library, it continues to
work with FreeTDS.  (Whew!)

BTW, the issue Ted Hayes raise is still broken; my first attempted fix was
wrong.  t0018 works fine with Microsoft's db-lib.  

If anyone else is interested in working on this, I'm happy to share my
nmake-compatible Makefile.  

More ahead.  

--jkl