Patch for psql 8.0, 8.1 and 8.2 backwards compatibility

"Ugh, I started the wrong version of psql again".

This patch offers basic backwards compatibility, so a version 8.4 psql 
can successfully do common operations on Postgres 8.0, 8.1, 8.2 and 
8.3.  I expect it's incomplete support, but as of yet I can't find an 
actual problem.  To me it is a step forward regardless, as it fixes "\d" 
which is pretty crucial even when just popping to an old server to check 
on something before an upgrade.

Notes:
1) Patched against cvs as of 19 May 2008.
2) The exact version numbers for the tweaks need help from a guru.
3) The usual version mismatch warning remains, as this is not a promise 
of full compatibility.

             Bryce Nesbitt


PS: See also:
http://archives.postgresql.org/pgsql-bugs/2005-08/msg00306.php
http://unixadmintalk.com/f47/improved-df-psql-backward-compatibility-345293/
http://archives.postgresql.org/pgsql-sql/2008-02/msg00088.php

? psql
Index: describe.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/bin/psql/describe.c,v
retrieving revision 1.173
diff -c -2 -r1.173 describe.c
*** describe.c	13 May 2008 00:23:17 -0000	1.173
--- describe.c	20 May 2008 05:16:33 -0000
***************
*** 804,810 ****
--- 804,818 ----
  	bool		show_modifiers = false;
  	bool		retval;
+     char       *indisvalid, *tgconstraint;   // Backwards compatibility differences
  
  	retval = false;
  
+     /*
+     ** Adjust queries for basic backwards compatibility
+     ** Should allow use with Postgres 8.0, 8.1, 8.2 servers.
+     */
+     indisvalid      = pset.sversion > 82000 ? "i.indisvalid" : "true";
+     tgconstraint    = pset.sversion > 81000 ? "AND t.tgconstraint = 0\n" : "";
+ 
  	/* This output looks confusing in expanded mode. */
  	myopt.expanded = false;
***************
*** 985,994 ****
  
  		printfPQExpBuffer(&buf,
! 						  "SELECT i.indisunique, i.indisprimary, i.indisclustered, i.indisvalid, a.amname, c2.relname,\n"
! 					"  pg_catalog.pg_get_expr(i.indpred, i.indrelid, true)\n"
! 						  "FROM pg_catalog.pg_index i, pg_catalog.pg_class c, pg_catalog.pg_class c2, pg_catalog.pg_am a\n"
! 		  "WHERE i.indexrelid = c.oid AND c.oid = '%s' AND c.relam = a.oid\n"
! 						  "AND i.indrelid = c2.oid",
! 						  oid);
  
  		result = PSQLexec(buf.data, false);
--- 993,1002 ----
  
  		printfPQExpBuffer(&buf,
! 			"SELECT i.indisunique, i.indisprimary, i.indisclustered, %s , a.amname, c2.relname,\n"
! 			"  pg_catalog.pg_get_expr(i.indpred, i.indrelid, true)\n"
! 			"FROM pg_catalog.pg_index i, pg_catalog.pg_class c, pg_catalog.pg_class c2, pg_catalog.pg_am a\n"
! 			"WHERE i.indexrelid = c.oid AND c.oid = '%s' AND c.relam = a.oid\n"
! 			"AND i.indrelid = c2.oid",
! 			 indisvalid, oid);
  
  		result = PSQLexec(buf.data, false);
***************
*** 1087,1096 ****
  		{
  			printfPQExpBuffer(&buf,
! 							  "SELECT c2.relname, i.indisprimary, i.indisunique, i.indisclustered, i.indisvalid, "
! 							  "pg_catalog.pg_get_indexdef(i.indexrelid, 0, true), c2.reltablespace\n"
! 							  "FROM pg_catalog.pg_class c, pg_catalog.pg_class c2, pg_catalog.pg_index i\n"
! 							  "WHERE c.oid = '%s' AND c.oid = i.indrelid AND i.indexrelid = c2.oid\n"
! 			  "ORDER BY i.indisprimary DESC, i.indisunique DESC, c2.relname",
! 							  oid);
  			result = PSQLexec(buf.data, false);
  			if (!result)
--- 1095,1104 ----
  		{
  			printfPQExpBuffer(&buf,
! 				"SELECT c2.relname, i.indisprimary, i.indisunique, i.indisclustered, %s, "
! 				" pg_catalog.pg_get_indexdef(i.indexrelid, 0, true), c2.reltablespace\n"
! 	            "FROM pg_catalog.pg_class c, pg_catalog.pg_class c2, pg_catalog.pg_index i\n"
! 	            "WHERE c.oid = '%s' AND c.oid = i.indrelid AND i.indexrelid = c2.oid\n"
! 				"ORDER BY i.indisprimary DESC, i.indisunique DESC, c2.relname",
! 				 indisvalid,oid);
  			result = PSQLexec(buf.data, false);
  			if (!result)
***************
*** 1340,1347 ****
  							  "t.tgenabled\n"
  							  "FROM pg_catalog.pg_trigger t\n"
! 							  "WHERE t.tgrelid = '%s' "
! 							  "AND t.tgconstraint = 0\n"
  							  "ORDER BY 1",
! 							  oid);
  			result = PSQLexec(buf.data, false);
  			if (!result)
--- 1348,1354 ----
  							  "t.tgenabled\n"
  							  "FROM pg_catalog.pg_trigger t\n"
! 							  "WHERE t.tgrelid = '%s' %s"
  							  "ORDER BY 1",
! 							  oid,tgconstraint);
  			result = PSQLexec(buf.data, false);
  			if (!result)