Update docker-library

- `php`: fix some Apache woes (docker-library/php#43), and add `docker-php-ext-install` and `docker-php-ext-configure` (docker-library/php#41)
- `tomcat`: 7.0.57
- `wordpress`: push more of the PHP+Apache logic into `php` where it belongs (docker-library/wordpress#25), and update the image to use the new `docker-php-ext-install` magic for the extra core extensions it needs (docker-library/wordpress#26)