Avoid weak pointers to NSViewController and NSWindowController

This is not supported on 10.7 (and leads to a crash).
Checkin release notes
Workaround for ruby’s YAML.load

JSON should be a subset of YAML so we use ruby’s YAML parser to parse GitHub’s JSON. This however leads to syntax errors reported by the parser (as noted in issue #637) but if the JSON is “pretty printed” it seems to parse it fine (seems to be the extra white space for associative array pairs).

We can trick GitHub into pretty printing the JSON result by setting the user agent to be curl, so that is all this workaround does.