A few improvements to the `ready` script.

* fetch _all_ remotes (was missing upstream, which meant we didn’t merge
  all changes)
* fix origin branch check
* Switch to safer bash constructs – `$()` instead of backticks and
  `[[]]` instead of `[]`
Merge pull request #291 from sellout/ready/git-workflow-changes

A few improvements to the `ready` script.