pgsql: Updated text for bitmaps: < Bitmap indexes index single

Log Message:
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Updated text for bitmaps:

< Bitmap indexes index single columns that can be combined with other bitmap
< indexes to dynamically create a composite index to match a specific query.
< Each index is a bitmap, and the bitmaps are bitwise AND'ed or OR'ed to be
< combined. They can index by tid or can be lossy requiring a scan of the
< heap page to find matching rows, or perhaps use a mixed solution where
< tids are recorded for pages with only a few matches and per-page bitmaps
< are used for more dense pages. Another idea is to use a 32-bit bitmap
< for every page and set a bit based on the item number mod(32).

> This feature allows separate indexes to be ANDed or ORed together. This
> is particularly useful for data warehousing applications that need to
> query the database in an many permutations. This feature scans an index
> and creates an in-memory bitmap, and allows that bitmap to be combined
> with other bitmap created in a similar way. The bitmap can either index
> all TIDs, or be lossy, meaning it records just page numbers and each
> page tuple has to be checked for validity in a separate pass.

Modified Files:
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pgsql/doc:
TODO (r1.1501 -> r1.1502)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1501&r2=1.1502)
pgsql/doc/src/FAQ:
TODO.html (r1.8 -> r1.9)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.8&r2=1.9)