pgsql: Add: < > * Consider compressing indexes by storing key prefix

Log Message:
-----------
Add:

<

* Consider compressing indexes by storing key prefix values shared by
several rows as a single index entry

Modified Files:
--------------
pgsql/doc:
TODO (r1.1680 -> r1.1681)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1680&amp;r2=1.1681)
pgsql/doc/src/FAQ:
TODO.html (r1.187 -> r1.188)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.187&amp;r2=1.188)