Merging causes all PRs to appear as "Rebase needed"

[markhalliwell]

Current code is using the mergeable value provided in the PR JSON:
https://github.com/dreditor/dreditor.org/blob/7.x/sites/all/modules/custom/dreditor_org/dreditor_org.pages.inc#L62

https://github.com/dreditor/dreditor.org/blob/7.x/sites/all/modules/custom/dreditor_org/dreditor_org.pages.inc#L88-L94

This is fine, but we need to add an AJAX mechanism that checks the status of each PR until it's either mergeable or the latest (top) status returned by travis-ci is success: https://api.github.com/repos/dreditor/dreditor/statuses/283c7caaefeea05993a8058519c3942952164f15

[markhalliwell]

A temporary solution is to remove the dreditor_org_pull_requests entry in the {cache} table and force it to rebuild pull the PRs from GH's API (after the tests have finished re-checking everything).