Add an option to allow run regression test for individual module on Windows build

Hi Hackers,

When I was working on an extension on Windows platform, I used the
command 'vcregress contribcheck' to run the regression test for my
module. However, this command will run the regression test for all the
modules, I couldn't find a way to regress test my module only. I think
it would be better to have such an option to make the development be
more efficient (Maybe there is a solution already, but I can't find it).

The attached patch allow user to run the regression test by using either
'vcregress contribcheck' or 'vcregress contribcheck postgres_fdw' if you
want to test your extension directly, for example, 'postgres_fdw'.

--
David

Software Engineer
Highgo Software Inc. (Canada)
www.highgo.ca