tunnings for rake tasks on 4.0 (should now be working for built-in adapters)
update 4.0 and start testing agains AR-4.0 with travis-ci
refactored JdbcConnection - eliminated ConfigHelper + moved #active?
JdbcAdapter + connection tweaks
- support passing 2 args to #initialize
- do not force adapter_spec if set to nil
- prepare for doing #configure_connection on #reconnect!
- no need to #configure_connection when spec module extended
jdbc connection updates to better follow AR semantics
- active? should check whether connection is valid
- reconnect! should configure_connection if available
- use connection.isValid as fallback (no need for connection_alive_sql)

fixes #351
connection_alive_sql for sqlite3 - it's driver is not very  recent
thus likely not conforming to all of JDBC 4.0
update and fix  jndi tests (jndi callbacks test should not influence others)
fix incorrectly using JdbcAdapter's meta-class to call #arel2_visitor
AR::Base >= 2.3 always responds to connection_pool method
exclude (travis-ci) 4.0 tests on  JRuby 1.8 + run derby tests as well