setup the connection methods when (jdbc) adapter is loaded

(hopefully) finally correctly load drivers (this is most importantly a follow-up on 20522b6ce39a)

rake tests are now runnable - although far from green on Rails 3.2 : 

`rake rails:test DRIVER=sqlite3 RAILS=../rails`
```
Finished in 113.934 seconds.

3281 tests, 9463 assertions, 13 failures, 114 errors, 0 pendings, 0 omissions, 0 notifications
0% passed

28.80 tests/s, 83.06 assertions/s
```

`rake rails:test DRIVER=mysql RAILS=../rails`
```
Finished in 218.978 seconds.

3313 tests, 9525 assertions, 11 failures, 125 errors, 0 pendings, 0 omissions, 0 notifications
0% passed

15.13 tests/s, 43.50 assertions/s
```