publicize constructors + allow access to ALLOCATORs for potential overriders
re-implement `jndi_config?` helper as a native method
re-implement connection factory setup in "native" Java code (back-compat)

- jndi: connection configuration now allow for username/password overrides
refactor jndi (derby) tests - we'll be likely adding some more
do not require eagerly driver.rb - likely won't be used
no need to eagerly load the type converter - not needed with most adapters
some more JNDI testing - now with MySQL as well
setup test_jdbc and test_jndi prereqs
start cleaning up some of our testing code - so we can "share"'em later
synchronize setting resolved visitor type
useful to warn when visitor type is being overwriten ...

this might currently only happen when two connections are made using `adapter: jdbc` for different databases (connection specs)
clean visitor type since out jdbc test use adapter: jdbc  with various DBs
support manually setting (default) transaction isolation on connection for all
refactored jndi tests
warn when using `adapter: jdbc` configuration while there's a standalone 1
[derby] no longer forcing connection by default into serializable isolation
besides setting `adapter: jdbc` also `adapter: jndi` is deprecated
rake test_jndi now declares sub-jndi tests as prereqs
explicitly use runtime's java support to load driver's connection class
[mysql] switch to using the non-registering driver by default