Update location to download flex for building on Windows.

doc/src/sgml/install-win32.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/install-win32.sgml,v 1.53 2009/07/13 01:51:56 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/install-win32.sgml,v 1.54 2009/07/23 17:06:48 adunstan Exp $ -->
 
 <chapter id="install-win32">
  <title>Installation from Source Code on <productname>Windows</productname></title>
@@ -103,8 +103,9 @@
       Bison and Flex are required to build from CVS, but not required when
       building from a release file. Note that only Bison 1.875 or versions
       2.2 and later will work. Also, Flex version 2.5.31 or later is required.
-      Bison and Flex can be
-      downloaded from <ulink url="http://gnuwin32.sourceforge.net"></>.
+      Bison can be downloaded from <ulink url="http://gnuwin32.sourceforge.net"></>.
+      Flex can be downloaded from 
+      <ulink url="http://www.postgresql.org/ftp/misc/winflex/"></>.
      </para></listitem>
     </varlistentry>