pgsql: Add: * Allow star join optimizations While our bitmap scan

Log Message:
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Add:

* Allow star join optimizations

While our bitmap scan allows multiple indexes to be joined to get
to heap rows, a star joins allows multiple dimension _tables_ to
be joined to index into a larger main fact table. The join is
usually performed by either creating a cartesian product of all
the dimmension tables and doing a single join on that product or
using subselects to create bitmaps of each dimmension table match
and merge the bitmaps to perform the join on the fact table.

Modified Files:
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pgsql/doc:
TODO (r1.1730 -> r1.1731)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1730&r2=1.1731)
pgsql/doc/src/FAQ:
TODO.html (r1.235 -> r1.236)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.235&r2=1.236)