Using g.yaml with a file that doesn't exist or misformatting a yaml document throws grow into a error state

[jeremydw]

You can throw the development server into a stuck error state with the following:

foo: !g.yaml /content/to/bad/file.yaml

or by making a sytax error in a yaml file.

Either issue requires a restart of Grow to fix it. We should catch YAML parsing errors, bubble them up (as we do now), and allow users to fix YAML without a restart.

[Zoramite]

I don't think this is still an issue, but if it is we can reopen it.