Added a stripModifiers() function to remove shared|const|immutable storage classes in D2 (should eventually be moved to a dhelpers file rather than llvm helpers). Replaced a few occurances of STCinvariant with STCimmutable.

module arrays3;

void main()
{
    int[] arr;
    {arr = new int[25];}
    {assert(arr.length == 25);}
    {arr.length = arr.length + 5;}
    {assert(arr.length == 30);}
}