Attached closure-related test cases fail.

closure5w.d: Segfaults. Only f() creates a closure and 'dg = & i' does not get a
valid reference to it.

closure8w.d: Fails with ArrayBoundsError.

closure11w.d: Assert fails.  The tests in Function::needsClosure only
check f->isVirtual(), but a virtual function can call a non-virtual
function which does non-local access.  I fixed this in GDC by
testing f->isThis() instead.

closure13w.d: Assert fails. DotVarExp::semantic does not call
checkNestedReference for the 'this' of an outer function.
I fixed this in GDC by adding a semantic() call:

	// Skip over nested functions, and get the enclosing
	// class type.
	Dsymbol *s = tcd->toParent();
	while (s && s->isFuncDeclaration())
	{   FuncDeclaration *f = s->isFuncDeclaration();
	    if (f->vthis)
	    {
		e1 = new VarExp(loc, f->vthis);
	    }
	    s = s->toParent();
	}
	if (s && s->isClassDeclaration())
	    e1->type = s->isClassDeclaration()->type;

 +	e1 = e1->semantic(sc); // Added to get corrected nested refs
	goto L1;