Fix dblink_connect() so that it verifies that a password is supplied in the

conninfo string *before* trying to connect to the remote server, not after.
As pointed out by Marko Kreen, in certain not-very-plausible situations
this could result in sending a password from the postgres user's .pgpass file,
or other places that non-superusers shouldn't have access to, to an
untrustworthy remote server.  The cleanest fix seems to be to expose libpq's
conninfo-string-parsing code so that dblink can check for a password option
without duplicating the parsing logic.

Joe Conway, with a little cleanup by Tom Lane

src/interfaces/libpq/libpq-fe.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.143 2008/09/17 04:31:08 tgl Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.144 2008/09/22 13:55:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -164,6 +164,7 @@ typedef struct _PQprintOpt
 
 /* ----------------
  * Structure for the conninfo parameter definitions returned by PQconndefaults
+ * or PQconninfoParse.
  *
  * All fields except "val" point at static strings which must not be altered.
  * "val" is either NULL or a malloc'd current-value string.  PQconninfoFree()
@@ -177,7 +178,7 @@ typedef struct _PQconninfoOption
 	char	   *compiled;		/* Fallback compiled in default value	*/
 	char	   *val;			/* Option's current value, or NULL		 */
 	char	   *label;			/* Label for field in connect dialog	*/
-	char	   *dispchar;		/* Character to display for this field in a
+	char	   *dispchar;		/* Indicates how to display this field in a
 								 * connect dialog. Values are: "" Display
 								 * entered value as is "*" Password field -
 								 * hide value "D"  Debug option - don't show
@@ -243,7 +244,10 @@ extern void PQfinish(PGconn *conn);
 /* get info about connection options known to PQconnectdb */
 extern PQconninfoOption *PQconndefaults(void);
 
-/* free the data structure returned by PQconndefaults() */
+/* parse connection options in same way as PQconnectdb */
+extern PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);
+
+/* free the data structure returned by PQconndefaults() or PQconninfoParse() */
 extern void PQconninfoFree(PQconninfoOption *connOptions);
 
 /*