This could be triggered when passing an array with "holes" to variadic commands.
Connection classes based on the protocol serialized exposed by phpiredis were
not affected by this bug.
Fixes#316.
We now have a base test case class for Predis (namely PredisTestCase)
grouping various commonly used utility methods shared by all of the
tests in the suite, greatly improving reusability.
Daniele Alessandri