The attached patch fixes configure to detect libpq on Windows boxes.
Unfortunately it is necessary to explicitly specify the appropriate
options on the command line (with msys/unix style paths) because
pg_config returns semi-DOS style paths (such as
C:/msys/1.0/local/pgsql/include) which GCC doesn't like.

I haven't included an updated version of configure as I only have
autoconf 2.59 on Windows, and wasn't sure if an update would be
accepted. I can supply it if required though.

Regards, Dave Page
