Fix for crash bug caused by Iframe NULL reference

https://github.com/ariya/phantomjs/issues/10947
https://github.com/ariya/phantomjs/issues/11103
https://github.com/ariya/phantomjs/pull/11984
Add example for how to post a json request to HTTP server

https://github.com/ariya/phantomjs/issues/11969
Adding "test/ghostdriver-test" to run in Travis CI

Related to issue #11880
Making GhostDriver test "quiet-er" (and parallel)

Also, trying to get the exit status of those tests reported, in case they fail.
Sorting out parallel testing for GhostDriver

Related to #11952.
Removed a flaky (and pointless) test

Related to #11952.
Run PhantomJS's tests as part of TravisCI