Update bison warning to be clearer about its purpose.

configure

@@ -4107,11 +4107,11 @@ done
 if test "$YACC"; then
   if $YACC --version | sed q | $AWK '{ if ($4 < 1.875) exit 0; else exit 1;}'; then
     { echo "$as_me:$LINENO: WARNING:
-*** The installed version of Bison is too old.  PostgreSQL needs
-*** Bison version 1.875 or later." >&5
+*** If you are going to modify the lexer files or build from CVS, the installed
+*** version of Bison is too old.  Bison version 1.875 or later is required." >&5
 echo "$as_me: WARNING:
-*** The installed version of Bison is too old.  PostgreSQL needs
-*** Bison version 1.875 or later." >&2;}
+*** If you are going to modify the lexer files or build from CVS, the installed
+*** version of Bison is too old.  Bison version 1.875 or later is required." >&2;}
   fi
 fi
 

configure.in

 dnl Process this file with autoconf to produce a configure script.
-dnl $PostgreSQL: pgsql/configure.in,v 1.316 2004/02/11 21:44:04 momjian Exp $
+dnl $PostgreSQL: pgsql/configure.in,v 1.317 2004/03/02 20:08:52 momjian Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -559,8 +559,8 @@ AC_CHECK_PROGS(YACC, ['bison -y'])
 if test "$YACC"; then
   if $YACC --version | sed q | $AWK '{ if ($4 < 1.875) exit 0; else exit 1;}'; then
     AC_MSG_WARN([
-*** The installed version of Bison is too old.  PostgreSQL needs
-*** Bison version 1.875 or later.])
+*** If you are going to modify the lexer files or build from CVS, the installed
+*** version of Bison is too old.  Bison version 1.875 or later is required.])
   fi
 fi