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 comma;

void main()
{
    int i=0,j=0;
    for (; i<10; i++,j++)
    {
    }
    assert(i == 10);
    assert(j == 10);
}