pgsql: Add URL for: * Allow accurate statistics to be collected on

Log Message:
-----------
Add URL for:

* Allow accurate statistics to be collected on indexes with more than
one column or expression indexes, perhaps using per-index statistics

http://archives.postgresql.org/pgsql-hackers/2007-03/msg01131.php

Modified Files:
--------------
pgsql/doc:
TODO (r1.2122 -> r1.2123)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.2122&r2=1.2123)
pgsql/doc/src/FAQ:
TODO.html (r1.623 -> r1.624)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.623&r2=1.624)