Rewrite of NSView display methods

[Fred Kiefer]

While studying the  EPS creation problem (#13140), I had a look at the 
different display methods on NSView. There is a lot of code duplication 
going on there and I would like to merge most of them together. For 
example have all the IfNeeded methods just check the flag and call their 
corresponding none checking method and similar rework. This would result 
in each simple display method using about three more method invokations 
then before. This may result in a tiny slow down (which I doubt anybody 
would notice), but also in cleaner, cosnsitent and easier to maintain 
code. Are there any objections to this change?

Merging the code raises the question, which of the two main 
implementations (displayRectIgnoringOpacity:, or 
displayIfNeededInRectIgnoringOpacity:) has the correct code? I think the 
later one.
And why is there extra handling in displayIfNeededIgnoringOpacity?

Cheers
Fred