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.

class C { void foo() {} }

void main()
{
  C c = new C;
  void delegate() dlg = &c.foo;

  assert(dlg);
}