%ENV warnings during builds

Hi folks

It looks like pgflex.bat and pgbison.bat in the win32 build files would 
benefit from a tweak to eliminate a complaint from Perl.

Perl emits the error:
  Hash %ENV missing the % in argument 1 of each() at -e line 1

on the lines that process buildenv.pl. This is because % in batch files 
is processed differently to on the command line. (Yes, that's stupid). 
Quoting doesn't affect this. Percent signs in batch files that are 
intended to be literals should be doubled, so %ENV should be written %%ENV.

http://support.microsoft.com/kb/75634

I. Hate. Batch. Files.

--
Craig Ringer