Added a Vagrantfile and fixed 2 mysql-related bugs

1. I added `Vagrantfile` that sets up the all necessary environment to contribute the project (including mysql).

Usage:

    vagrant up
    # wait several minutes to download and install everything
    vagrant ssh
    cd /vagrant
    bin/phpunit # all tests must puss, there should be no skipped tests

2. I fixed a bug with instantiating multiple data sources in tests. Seems like it has been broken for ages - you just could not instantiate more than one different database in unit tests

3. I fixed `TRUNCATE` behaviour for mysql - the `dbunit` unit tests were also affected

Now everything passes and nothing is skipped:

    vagrant@precise64:/vagrant$ bin/phpunit
    PHPUnit 4.0.12 by Sebastian Bergmann.

    Configuration read from /vagrant/phpunit.xml

    ................................................................. 65 / 87 ( 74%)

    ......................

    Time: 15.35 seconds, Memory: 30.25Mb

    OK (87 tests, 182 assertions)

    Generating code coverage report in Clover XML format ... done

    Generating code coverage report in HTML format ... done