Message 169629 - Python tracker

I'm attaching a patch, which solves the issue. Patch intoduces new argument "preserve_permissions" for extract and extractall methods. That argument may accept one of the three values: do not preserve permissions, preserve a safe subset of them or preserve all permissions. Three constants introduced for these options. Patch also contains test and docs. Tests pass for me on OS X 10.5, but I'm not sure if they'll pass on other operating systems.