Adding the Ability to Set the MySql Port

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #767, #153
| License       | MIT
| Doc PR        | http://www.php.net/manual/en/ref.pdo-mysql.php#ini.pdo-mysql.default-socket