RESET SESSION

This is draft version, for discussion.

New commands:

CLOSE ALL
DEALLOCATE ALL
RESET PLANS
RESET TEMPS -- please suggest better name

RESET SESSION

So in the end RESET SESSION basically executes following commands:

ABORT;
DEALLOCATE ALL;
CLOSE ALL;
RESET ALL;
SET SESSION AUTHORIZATION DEFAULT;
UNLISTEN *;
RESET TEMPS;
RESET PLANS;

I think CLOSE ALL and DEALLOCATE ALL are useful in their own,
without considering poolers. They just make user lives easier.
The ALL just fits there.

RESET PLANS and RESET TEMPS are for the principle that components
for RESET SESSION should be available for users for special-case
situations and fine-tuning poolers. Also they add very little complexity.
(RESET PLANS could be useful its awn also).

Todo:

* Docs
* Disallow some commands inside TX?
* DEALLOCATE PREPARE ALL gives bison conflicts. is it needed?
* Send more details to client. Variants:
- CommandComplete: "RESET XXX", "CLOSE ALL", "DEALLOCATE ALL"
(CLOSE name and DEALLOCATE name would be good in normal case too,
that help anyone who wants to track what exists)
- RESET SESSION should send ParamStatus of all parms

--
marko