Fixed Bug with overloaded Array prototype

If Array prototype is extended by additional methods

    Array.prototype.bla = function ...

these attribute names (bla) show up as key on

    for i in theArrayVar -> [0, 1, 2, ..., 'bla']

This obviously results in errors when trying to access this value

    theArrayVar[i]

The good old

    for (var i; i < a.length, i++)

is safer here.