pgsql: Add all heap page rows visible bitmap idea: < the heap.

Log Message:
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Add all heap page rows visible bitmap idea:

< the heap. One way to allow this is to set a bit to index tuples
> the heap. One way to allow this is to set a bit on index tuples
< be cleared when a heap tuple is expired.
<
> be cleared when a heap tuple is expired. Another idea is to maintain
> a bitmap of heap pages where all rows are visible to all backends,
> and allow index lookups to reference that bitmap to avoid heap
> lookups, perhaps the same bitmap we might add someday to determine
> which heap pages need vacuuming.

Modified Files:
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pgsql/doc:
TODO (r1.1708 -> r1.1709)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1708&r2=1.1709)
pgsql/doc/src/FAQ:
TODO.html (r1.215 -> r1.216)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.215&r2=1.216)