Optimization for the duplicate paintop

[Casper Boemann]

Well actualy in this particular case using the non-exact version means that 
the rect is less than the rect actually is - which is bad

the function is "negated" which is why it would fail.

----- Original Message ----- 
From: "Boudewijn Rempt" <boud at valdyas.org>
The drawback is that the rect then is aligned with tile boundaries -- which
means that it is larger than the rect really is. This may not matter too 
much
in this particular case. It means that more pixels are considered for
compositing, and then discarded, but that may well be less costly than my
(stupid, simple-minded, straightforward, unoptimized) algorith for
calculating the exact rect.

We use extactRect in many places, though, and optimizing it would be a great
idea.