Source code cleanup

I'm getting a bunch of compiler warnings when I compile the latest
psqlodbc sources from CVS. I spent some time cleaning those up.

I also got access to a report of a Coverity scan over psqlodbc source
tree. That found a bunch of additional issues, some of which were
genuine (minor) bugs. I'm still in the process of going through the
report, but I fixed some bugs already.

I also wrote a small regression test suite to test with. It only tests a
few of the ODBC functions at the moment, but it's better than nothing,
and it can be easily extended. What do others use for testing psqlodbc?

I pushed the result to a git repository at
git@github.com:hlinnaka/psqlodbc.git. It contains the psqlodbc CVS
history, as converted by git cvsimport, and my changes as commits on top
of that. I can also send the changes as patches if that's preferred. Let
me know how to proceed.

- Heikki