Make session handling compatible to any PHP session handler
Today there's no possibility to get Flow working with a custom php session save handler like redis or memcached. You can define one in your php.ini but Flow tries to create the session_save_path as a folder if it doesn't exist. This leads to something like this:
Uncaught Exception Could not create directory "tcp://127.0.0.1:6379"!
Flow, Y U no Redis? ;)
My solution would be to add an option called "TYPO3:Flow:session:PhpSession:saveHandler" in the Settings.yaml and set this to "file" as default. Also there should be a small check, if the save_handler is still "file", before trying to create some sesssion storage folders in TYPO3\Flow\Session\PhpSession (in initializeObject and destroyAll). Then it's easy for Flow users to switch to a redis save handler f.e. and get it up running without an exception.