Caches should be flushed on package version number changes
Usually when upgrading from one FLOW3 version to another the user will experience a PHP fatal error because some interfaces (or other code parts) changed which are not compatible with cached code (eg. the AOP proxy classes). Therefore we need a new cache which stores information about all active packages - as a start that could be simply the version number or even a hash of all version numbers. On initializing the cache framework, this information should be compared with the actual values and if they don't match all caches should be flushed.