* delete a ResourceOwner (including child owner objects); all resources

must have been released beforehand

This API directly supports the resource types listed in the definition of

ResourceOwnerData struct in src/backend/utils/resowner/resowner.c.

Other objects can be associated with a ResourceOwner by recording the address

of the owning ResourceOwner in such an object. There is an API for other

modules to get control during ResourceOwner release, so that they can scan

their own data structures to find the objects that need to be deleted.

Locks are handled specially because in non-error situations a lock should

be held until end of transaction, even if it was originally taken by a

subtransaction or portal. Therefore, the "release" operation on a child

ResourceOwner transfers lock ownership to the parent instead of actually

releasing the lock, if isCommit is true.

Currently, ResourceOwners contain direct support for recording ownership of

buffer pins, lmgr locks, and catcache, relcache, plancache, tupdesc, and

snapshot references. Other objects can be associated with a ResourceOwner by

recording the address of the owning ResourceOwner in such an object. There is

an API for other modules to get control during ResourceOwner release, so that

they can scan their own data structures to find the objects that need to be

deleted.

Whenever we are inside a transaction, the global variable

CurrentResourceOwner shows which resource owner should be assigned

ownership of acquired resources. Note however that CurrentResourceOwner