More vcbuild

* Add support for building postgres.bki.

* Add a genbki.pl script to do this. This could possibly be used in
place of the shellscript for the unix build as well, sometime in the
future, but not for 8.2.

* Add install.pl that will partially do what "make install" does. Does
not yet install the datafiles from contrib, but I think that's the only
major thing missing. (Apart from no documenation build that is, but we
don't build that at all ATM so there's nothing to install)

* Add clean.bat


New files go in src/tools/msvc, of course.

//Magnus