Remove the 64K limit on the lengths of keys and values within an hstore.
(This changes the on-disk format, but the old format can still be read.)
Add support for btree/hash opclasses for hstore --- this is not so much
for actual indexing purposes as to allow use of GROUP BY, DISTINCT, etc.
Add various other new functions and operators.
Andrew Gierth
with minor editorization by me.
Hstore improvements
* add operation hstore ? text - excat equivalent of exist()
* remove undocumented behaviour of contains operation with NULL value
* now 'key'::text=>NULL returns '"key"=>NULL' instead of NULL
* Add GIN support for contains and exist operations
* Add GiST support for exist operatiion
* improve regression tests
