Get a patch for two commits

Produces a raw patch for a single commit (diffed against its first parent), or a patch-series for a revspec of 2 commits (e.g. 3a8b42..9ff173 where the first commit represents the source and the second commit the destination).

In case of the latter (diffing a revspec), a patch series is returned for the commits on the source branch (3a8b42 and its ancestors in our example).

While similar to diffs, patches:

• Have a commit header (username, commit message, etc)
• Do not support the path=foo/bar.py query parameter

The raw patch is returned as-is, in whatever encoding the files in the repository use. It is not decoded into unicode. As such, the content-type is text/plain.