pgsql: Update bitmap index entries: < * Allow the creation of bitmap

Log Message:
-----------
Update bitmap index entries:

< * Allow the creation of bitmap indexes which can be quickly combined
< with other bitmap indexes
> * Allow non-bitmap indexes to be combined by creating bitmaps in memory
259,261c258,259
< combined. Such indexes could be more compact if there are few unique
< value. Also, perhaps they can be lossy requiring a scan of the heap page
< to find matching rows.
> combined. They can index by tid or can be lossy requiring a scan of the
> heap page to find matching rows.
263c261,262
< * Allow non-bitmap indexes to be combined
> * Allow the creation of on-disk bitmap indexes which can be quickly
> combined with other bitmap indexes
265,266c264
< Do lookups on non-bitmap indexes and create bitmaps in memory that can be
< combined with other indexes.
> Such indexes could be more compact if there are few unique value.

Modified Files:
--------------
pgsql/doc:
TODO (r1.1377 -> r1.1378)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1377&r2=1.1378)