minor README updates
[postgres] we should return "raw" hstore values on AR < 4.0 by default
(regression caused by fixing #454 for AR >= 4.0)
avoid using PG_VERSION in a test-case (since global const was moved)
Added failing test for multiple savepoints
when "pop-ing" current savepoint name - consider open transaction count

- this allows us to work with user marked savepoints as intended, since they will likely execute within a single AR transaction object
- but at the same time AR's nested transaction emulation (using savepoints) will work in a Rails compatible way (fixes #477)
re-build jar - prepare for 1.3.2
test needs one more reset as it might keep to incorrect column type (PS=t)