vcbuild install

This patch changes the installscript for vcbuild to actually parse the
generated solution files for what to install, instead of blindly copying
everything as it previously did. With the previous quick-n-dirty
version, it would copy old DLLs if you reconfigured in a way that didn't
include subprojects like a PL for example.

The part of install.pl previously included in my pgregress patch (not
yet applied) are superseded by and included in this patch (only the
install.pl part is - the changes to the other build files and to the C
file are still very much current)

//Magnus