vcbuild updates from Magnus:

* After Markos patch, now builds pgcrypto without zlib again
* Updates README with xml info
* xml requires xslt and iconv
* disable unnecessary warning about __cdecl()
* Add a buildenv.bat called from all other bat files to set up things
like PATH for flex/bison. (Can't just set it before calling, doesn't
always work when building from the GUI)