Work with issues in upstream repositories

[rprouse]

A common GitHub workflow is to fork a repository to work on an issue. As it stands, if you don't have commit rights to the upstream repository, you cannot use this extension to work with those issues. It would be nice to pull in issues from the upstream repository.

You might not always want to pull in upstream issues though, so how do we do it? Possibilities are,

• Add upstream repositories to the repository list. This might cause problems if we start auto selecting the repository based on the code you are working on.
• When you select the fork repository, show issues for the upstream. This could be a global or per-repository option.
• Show issues for both the fork and for the upstream in the same window. If you create new issue, which does it go to?