Added phpdoc for TestCase::getMock

Texts inspired from the doc: http://phpunit.de/manual/3.7/en/test-doubles.html
Merge pull request #1069 from mnapoli/patch-1
Try running unit tests on HHVM
Merge pull request #1072 from ptarjan/patch-1

Try running unit tests on HHVM
HHVM is failing

While we iron out the travis issues, allow this to fail
Merge pull request #1073 from ptarjan/patch-2

HHVM is failing
Merge branch '3.7'