TODO list updates

In reading through the TODO list, I noticed a few things that I think
are done, may be done, or may be partially done.  See below.
Thoughts?  ...Robert

Add missing operators for geometric data types
- this is at least partly done.  not sure if it is entirely done.

Add OR REPLACE to CREATE LANGUAGE
- Done.

Implement full support for window framing clauses.
- Not sure if we made any progress on this or not.

Add PQescapeIdentifierConn()
- Done, as PQescapeIdentifier().

Add UNIQUE capability to non-btree indexes
- This is one application of exclusion constraints, so I'd say this is done.

[GIN] Support empty indexed values (such as zero-element arrays) properly
- I think this might be done but I'm not sure.

Clean up VACUUM FULL's klugy transaction management
- I think this is moot with the new cluster-based VF.