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
this effort (someday) is likely going to end up as 1.4.0
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