Allow setting system user and group IDs for spawned processes (proposed)

[dluxemburg]

Currently the spawned git child processes all belong to the user/group of the parent process. This prevents using Simple Git on files owned by other uses without changing file ownership.

So, support a spawnOptions configuration option that passes through supported values (just uid and gid) to the child_process.spawn call that ultimately invokes git.

I made this work with a plugin modeled on the way custom config options get passed to the git command because that seemed like the most similar existing behavior. I am happy to switch this to the way environment variables work if that's more appropriate.

[steveukx]

Hi, thank you for opening the pull request.

This all looks good to me, I'll include it with the next release this weekend. You can follow #638 to see when it has been published to npm.

[dluxemburg]

That's great! Thank you for making/maintaining this.