Replace call_user_func_array(), part 2

Replace call_user_func_array(), part 2

Uses new PHP 5.6 syntax like ...parameter unpacking and
calling anything looking like a callback to make the code more readable.
There are much more occurrences but this commit is intentionally limited
to an easily reviewable size.

In one occurrence, a simple conditional instead of trickery was much more readable.

This patch finishes all the easy stuf in the core, the remainder is either unobvious
or would result in smaller readability gains. It will be carefully dealt with in
further commits.

Change-Id: I79a16c48bfb98b75e5b99f2f6f4fa07b3ae02c5b