Clean filtered objects if the entire batch was filtered away, to prevent memory allocation issue.
Removed the testing on Symfony dev-master

dev-master is Symfony 3.0, and we are not yet marking it as compatible
Merge branch '3.0.x'

Conflicts:
	.travis.yml

Duplicate testing on Symfony 2.6 is removed (it is already done by the
normal testing as it is the latest stable), and testing on 2.4 is
removed again because it is EOLed.