Improve parser so that we can show an error cursor position for errors

during parse analysis, not only errors detected in the flex/bison stages.
This is per my earlier proposal.  This commit includes all the basic
infrastructure, but locations are only tracked and reported for errors
involving column references, function calls, and operators.  More could
be done later but this seems like a good set to start with.  I've also
moved the ReportSyntaxErrorPosition logic out of psql and into libpq,
which should make it available to more people --- even within psql this
is an improvement because warnings weren't handled by ReportSyntaxErrorPosition.

src/interfaces/libpq/libpq-int.h

@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.111 2006/03/05 15:59:10 momjian Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.112 2006/03/14 22:48:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -278,6 +278,7 @@ struct pg_conn
 	PGAsyncStatusType asyncStatus;
 	PGTransactionStatusType xactStatus;		/* never changes to ACTIVE */
 	PGQueryClass queryclass;
+	char	   *last_query;		/* last SQL command, or NULL if unknown */
 	bool		options_valid;	/* true if OK to attempt connection */
 	bool		nonblocking;	/* whether this connection is using nonblock
 								 * sending semantics */