Upgrade to 4.3.1-pending

- Document supported Plone version change in README.rst.
- Extend remote Plone 4.3.1-pending versions.cfg in base.cfg.
- Upgrade "core aclark components" e.g. Pillow, buildout.bootstrap, distribute, zc.buildout, etc.
- Remove hotfix(es).
- Upgrade PFG to recently patched release.
- Fix hostname in database.cfg to Cloudflare's non-proxied alias direct.plone.org.
- Remove buildout.dumppickedversions extension, functionality now included with zc.buildout.
- Add content ratings sources.
- Test upgrade locally just prior to this commit.
- Note: upgrade takes about 45 minutes to an hour to run, plan to disable logins on plone.org during deployment.
- Needed: contentratings and plone.contentratings releases.