Fix ContextTest comparison of ContextActivities signatures.

[pondermatic]

The grouping array was sent as argument 2 to the $contextActivities2 constructor. ContextActivities->__construct() only takes one argument and will not assign ANY properties if there is not exactly one argument. This cause $contextActivities2 to have a different number of parents than $contextActivities1. I believe the intent of 'contextActivities only: mismatch' and 'full: contextActivities mismatch' cases is to detect differences in the number of contextActivities->grouping objects.

[pondermatic]

#96 should be merged first in order to pass PHP 7 and HHVM tests.