more improvements to release notes

This patch makes a bunch of improvements to the release notes. I only
modified release.sgml -- HISTORY will need to be regenerated.

I was able to remove almost all of the "Other uncategorized" release
note entries, but left a few that I wasn't sure what to do with. We
should remove this section, and move the remaining entries to other
sections if necessary.

I had a few questions on some of the entries:

What is the following release note entry supposed to mean? "FETCH 0"
doesn't "do nothing", it now fetches the current cursor row. Bruce,
could you clarify this please?

     * MOVE/FETCH 0 now does nothing; return value of MOVE/FETCH 1/0
       varies based on the current offset in the cursor

This entry is plainly wrong:

     * Cause FETCH 1 to return the current cursor row, or zero if at
       beginning/end of cursor, per SQL spec (Bruce)

FETCH 0 is what actually returns the current cursor row, and returning
"zero" when a row value is expected wouldn't make much sense. I've
changed it to just say:

     * Cause FETCH 0 to return the current cursor row, per SQL spec
(Bruce)

If I've missed some of the intent of the original entry, let me know.

These two entries are duplicates, right?

     * Have SHOW DATESTYLE generate output similar to that used by SET
       DATESTYLE (Tom)
     * Change DATESTYLE to output its value in a more common format
(Tom)

I wasn't sure, so I didn't make this change in the patch.

-Neil