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)

src/tools/msvc/Solution.pm

@@ -14,6 +14,11 @@ sub new {
         strver   => '',
     };
 	bless $self;
+	if ($options->{xml}) {
+      if (!($options->{xslt} && $options->{iconv})) {
+         die "XML requires both XSLT and ICONV\n";
+      }   
+   }
 	return $self;
 }