Redis::mGet() & co. should be declared as variadic

[nicolas-grekas]

On PHP >5.6,

php > $r = new ReflectionMethod('Redis', 'mget');
php > var_dump($r->isVariadic());
bool(false)

This should return true.

[michael-grunder]

I'm not totally clear on how this works in the Zend api but I think it has to do with how arguments are defined. Because phpredis has so many methods it's not a small project.

Good news is that a lot of functions are generic so it is doable. We'll look at it for the next release.

[yatsukhnenko]

#1055