Fixes: #299 - mysql transactions and pooling

Please, for the love of god, merge! :) No pressure.

But, on a serious note, I have one failing test on this branch but it also fails for me on master too, the exact same test. Therefore, I don't think it's related, but if any of you guys have any ideas I'm all ears. Related to nonces.

```
not ok test/run/integration_tests.js .................. 35/36
    not ok 28 fresh nonce is accepted
      ---
        file:   /home/chilts/src/chilts-fxa-auth-server/test/run/integration_tests.js
        line:   388
        column: 21
        stack:  
          - getCaller (/home/chilts/src/chilts-fxa-auth-server/node_modules/tap/lib/tap-assert.js:418:17)
          - assert (/home/chilts/src/chilts-fxa-auth-server/node_modules/tap/lib/tap-assert.js:21:16)
          - Function.equal (/home/chilts/src/chilts-fxa-auth-server/node_modules/tap/lib/tap-assert.js:162:10)
          - Test._testAssert [as equal] (/home/chilts/src/chilts-fxa-auth-server/node_modules/tap/lib/tap-test.js:87:16)
          - Request._callback (/home/chilts/src/chilts-fxa-auth-server/test/run/integration_tests.js:388:21)
          - Request.self.callback (/home/chilts/src/chilts-fxa-auth-server/node_modules/request/request.js:129:22)
          - Request.EventEmitter.emit (events.js:98:17)
          - Request.<anonymous> (/home/chilts/src/chilts-fxa-auth-server/node_modules/request/request.js:873:14)
          - Request.EventEmitter.emit (events.js:117:20)
          - IncomingMessage.<anonymous> (/home/chilts/src/chilts-fxa-auth-server/node_modules/request/request.js:824:12)
        found:  401
        wanted: 200
...
```

I haven't yet figured it out, but happy to keep cracking on it, though as I said I get the exact same test failure on master. If @rfk or @dcoates can run all tests on this branch without failure then I guess it's my problem somewhere. :)

Thanks.