Fix Travis CI configuration

- Remove phantom build included in previous commit
- Finish quickly in case of errors
Remove link integrity tests as they are Products.PloneTestCase-based and I have no intention of maintain them (refs. #410)
Make a saner control of version pinning
Merge branch 'master' into issue_407

Conflicts:
	versions-4.2.x.cfg
	versions-4.3.x.cfg