Derive PartialOrd, Ord and Hash for bitflags types.

In order to prevent users from having to manually implement Hash and Ord for
bitflags types, this commit derives these traits automatically.

This breaks code that has manually implemented any of these traits for types
created by the bitflags! macro. Change this code by removing implementations
of these traits.

[breaking-change]
Implement Default for std::io::FilePermission