Maintain backwards compatibility for bitflags types

[kjughx]

Between versions 0.17.x and git2-0.18.0, bitflags was updated from 1.x to 2.1 which reduced the amount of derived traits on bitflags types. This in turn broke backwards compatibility since now bitflags types no longer implement PartialOrd, Ord and Hash.

The changelog of bitflags 2.0.0 mentions that:

If you need to maintain backwards compatibility, you can derive the following yourself:
#[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Clone, Copy)]

This fixes #1095.

[ehuss]

Thanks! Can you say what your use case is for being able to order the flags?

[kjughx]

Perhaps minor thing, I wrote a program which displays a git status over a workspace which includes many repositories, and wanted the changes to be grouped by their status flag, i.e. first all new files, then all modified or whatever, but group them in sections based on status. A niche use case sure but not a reason to break backwards compatibility imho.

[ehuss]

Sounds good, thanks!