pgsql: Add idea on auto-cluster: < automatically access the heap

Log Message:
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Add idea on auto-cluster:

< automatically access the heap data too.

automatically access the heap data too. A third idea would be to
store heap rows in hashed groups.

Modified Files:
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pgsql/doc:
TODO (r1.1372 -> r1.1373)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1372&amp;r2=1.1373)