IE8: DialogUnderlay is opaque in IE7/standards mode

[bill]

See test_Dialog.html on IE8, set to IE7 compatibility mode. The DialogUnderlay hides everything behind it.

Works fine in the real IE7 and in IE8 (standards mode), although IE8 has another problem w/the dialog title (#8349).

[bill]

Turns out that

filter: opacity(50)

is now working in IE8 standards mode (and other versions of IE, and IE8 in compatibility mode), so we don't need the

-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";

clause anymore. As a matter of fact, when the -ms-filter appears after the filter clause, as in the case of this bug:

.dj_ie .dijitDialogUnderlay {
	filter: alpha(opacity=50);
	-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";
}

... then it breaks IE8 in IE7 compatibility mode (although true IE7 works). So I'm thinking to just remove all the -ms-filter clauses.

Perhaps we can just wontfix #7697 too.

[bill]

(In [16479]) Apparently IE8 has decided to support filter: just like IE6 and IE7, so no need for the -ms-filter clauses, which are actually interfering when IE8 is in IE7 compatibility mode.

Fixes #8470, refs #7658.

Note that DojoX dialog's underlay now works (refs #8090) but it still has other issues, namely that the dialog contents are hidden (ie, the dialog is all white)