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.