Fixes the warning emitted by mysqli when sqlstate is not set (yet?).
http://git.php.net/?p=php-src.git;a=blob;f=ext/mysqli/mysqli_prop.c;h=2d36336372b75922bd8fbf40c5c9054a5230c8a0;hb=HEAD#l36

Warning masks actual connection error.

 * license
 * author tags
 * doc blocks
 * new lines

This PR introduces a new PingableConnection interface and exposes
a ping method on \Doctrine\DBAL\Connection. For drivers where no
ping is supported, a \Doctrine\DBAL\ConnectionException is thrown.

 * push error handling down to when it occurs
 * WIP, as I am unable to trigger false currently

 * move supportedDriverOptions into setDriverOptions
 * make setDriverOptions private
 * support \MYSQLI_SERVER_PUBLIC_KEY on 5.5.0+

 * fix typo
 * remove fluent interface

 * introduced $_supportedDriverOptions to validate what is passed into the object
 * added `setDrivrOptions()` which sets the array and throws exceptions

- Fixed docblocks
- Removed return statements on void methods
- Cleaned up unused private / local variables
- Fixed license issues
- Removed SVN leftovers
- Fixed doctrine-project.org links
- Added line breaks before return statements