Feature: git:wrapper user when uploading git-ssh.sh

This is related to [#154](https://github.com/capistrano/sshkit/issues/154), [#191](https://github.com/capistrano/sshkit/issues/191), and probably others.

I'm trying to run all of the commands as a different user than the one I connect with, and it works in general with the following:

```
SSHKit.config.command_map = Hash.new do |hash, command|
hash[command] = "sudo -u deployuser #{command}"
end
```

But the git:wrapper task does an upload of git-ssh.sh file, which ends up with my user as the owner, not deployuser. The last line of the task then fails because it tries to run chmod on this file as deployuser.

Is there a way to control the permissions on upload? I'm not too familiar with this part of capistrano and the purpose of the git:wrapper/how it works, so maybe trying to play with the permissions on that file isnt the solution, but any kind of workaround or general guidance would be appreciated.