Change the layout test result search policy for Mac OS X to fit better with the idea of
newer OS versions improving on previous OS versions.
Reviewed by Dan Bernstein.
The results for the latest version of Mac OS X are placed in the "mac" directory. The
results for older versions of Mac OS X are structured as a series of overlays. When
running on Leopard, the results in "mac-leopard" are searched before those in "mac".
When running on Tiger, the results in "mac-tiger" are searched before those in
"mac-leopard" and "mac".
* Scripts/run-webkit-tests:
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@41702
268f45cc-cd09-0410-ab3c-
d52691b4dbfc