Update Rakefile to ease building all drivers and adapters

- all namespace now operates on drivers and adapters
- new drivers namespace operates only on drivers
- new adapters namespace operates only on adapters
Don't attempt to load the 1.3.0 unless on at least Java 1.7.
Revert to auto-loading driver jars

We have many clients that expect simply including the jdbc-* gems is
sufficient to ensure the actual JDBC driver is on the classpath.
While we want to move to requiring an intentional load_driver, or
loading the driver when it's actually needed at connection time,
we can't break compatibility in the 1.2.x series.

For now, if you want to explicitly tell the jdbc-* gems to not auto-load
the driver jars, set the Java system property arjdbc.skip.autoload to true.
Update Rakefile to ease building all drivers and adapters

- all namespace now operates on drivers and adapters
- new drivers namespace operates only on drivers
- new adapters namespace operates only on adapters
PostgreSQL connections default to current user

If no username is given in the configuration for a postgresql connection,
default to the currently logged in user (as given by the user.name Java
property).  Closes #257.
Merge pull request #294 from jruby/release_cleanup

Release cleanup
update derby to 10.8.3.0
Merge pull request #295 from kares/derby-10.8.3.0

update derby to 10.8.3.0
do not auto-require the driver + jdbc test needs derby as well