pgsql: Done: * -Add a warning when the free space map is too small

Log Message:
-----------
Done:

* -Add a warning when the free space map is too small

Modified Files:
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pgsql/doc:
TODO (r1.1458 -> r1.1459)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1458&r2=1.1459)