pgsql: Add: > * Auto-vacuum > o Move into the backend code > o Scan

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

* Auto-vacuum
o Move into the backend code
o Scan the buffer cache to find free space or use background writer
o Use free-space map information to guide refilling

Modified Files:
--------------
pgsql/doc:
TODO (r1.1401 -> r1.1402)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1401&r2=1.1402)