Adjust configure's handling of libedit to not look for a history.h file.

Per Bob Friesenhahn's report, this file is not supplied by some versions
of libedit, and even when it is supplied it seems to be just a link to
readline.h, so we don't need to include it anyway.
Also, ensure that we won't try to use a too-old version of Bison.
The previous coding would bleat but then use it anyway; better to invoke
the 'missing' script if any grammar files need to be rebuilt.

configure.in

 dnl Process this file with autoconf to produce a configure script.
-dnl $PostgreSQL: pgsql/configure.in,v 1.479 2006/10/03 22:18:22 tgl Exp $
+dnl $PostgreSQL: pgsql/configure.in,v 1.480 2006/10/04 22:31:13 tgl Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -594,25 +594,28 @@ AC_PROG_RANLIB
 AC_PATH_PROG(TAR, tar)
 PGAC_CHECK_STRIP
 
-AC_CHECK_PROGS(YACC, ['bison -y'])
-
-if test "$YACC"; then
-  if $YACC --version | sed q | $AWK '{ if ($4 < 1.875) exit 0; else exit 1;}'; then
-    AC_MSG_WARN([
-*** If you are going to modify the grammar files or build from CVS, the installed
-*** version of Bison is too old.  Bison version 1.875 or later is required.])
+if test -z "$YACC"; then
+  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 to use with PostgreSQL.
+*** Bison version 1.875 or later is required.])
+      YACC=""
+    fi
   fi
-fi
 
-if test -z "$YACC"; then
-  AC_MSG_WARN([
-*** Without Bison you will not be able to build PostgreSQL from CVS or
+  if test -z "$YACC"; then
+    AC_MSG_WARN([
+*** Without Bison you will not be able to build PostgreSQL from CVS nor
 *** change any of the parser definition files.  You can obtain Bison from
 *** a GNU mirror site.  (If you are using the official distribution of
-*** PostgreSQL then you do not need to worry about this because the Bison
+*** PostgreSQL then you do not need to worry about this, because the Bison
 *** output is pre-generated.)  To use a different yacc program (possible,
 *** but not recommended), set the environment variable YACC before running
 *** 'configure'.])
+  fi
 fi
 AC_SUBST(YFLAGS)
 
@@ -753,13 +756,10 @@ if expr x"$pgac_cv_check_readline" : 'x-ledit' >/dev/null ; then
 If you have libedit already installed, see config.log for details on the
 failure.  It is possible the compiler isn't looking in the proper directory.
 Use --without-readline to disable libedit support.])])])])
-  AC_CHECK_HEADERS(editline/history.h, [],
-        [AC_CHECK_HEADERS(history.h, [],
-                [AC_CHECK_HEADERS(readline/history.h, [],
-                        [AC_MSG_ERROR([history header not found
-If you have libedit already installed, see config.log for details on the
-failure.  It is possible the compiler isn't looking in the proper directory.
-Use --without-readline to disable libedit support.])])])])
+# Note: in a libedit installation, history.h is normally a dummy, and may
+# not be there at all.  The functions are declared in readline.h instead.
+# To avoid including incompatible headers when both libraries are present,
+# assume we do not need history.h.
 fi
 
 if test "$with_zlib" = yes; then

src/include/pg_config.h.in

@@ -101,9 +101,6 @@
 /* Define to 1 if you have the `dlopen' function. */
 #undef HAVE_DLOPEN
 
-/* Define to 1 if you have the <editline/history.h> header file. */
-#undef HAVE_EDITLINE_HISTORY_H
-
 /* Define to 1 if you have the <editline/readline.h> header file. */
 #undef HAVE_EDITLINE_READLINE_H