PHP 5.3 compatibility

We need to remove the "middleware abstract definitions" for php 5.3 compatibility otherwise we get hit with "Can't inherit abstract function Clockwork\\Storage\\StorageInterface::store() (previously declared abstract in Clockwork\\Storage\\Storage" - see http://stackoverflow.com/questions/17525620/php-fatal-error-cant-inherit-abstract-function#answer-22521203 for more information.
Merge pull request #73 from hailwood/patch-1

PHP <5.3.9 compatibility for abstract methods.