Change precedence of reference union

["David A. Wheeler" <dwheeler@dwheeler.com>]

Excel's documentation at http://support.microsoft.com/kb/25189/EN-US/ ) claims that its precedence is (from highest to lowest) Range, Intersection, Union in that order. I've
checked, and it's true for Excel 2003.

I propose we change to this precedence order in the spec.  Basically, this swaps the precedence of intersection and union in the current spec.  I've added tests that check for this precedence in the next draft.  Good news, we now have at least some tests for all precedences, AND our precedence list now matches that document.

My apologies to all; it turns out my spam catcher has been labelling some messages as spam, so I didn't see them.  Eike Rathke sent us a message about this a long time back, but since I didn't see it, I didn't respond to it.

--- David A. Wheeler