Fixed the installation of HHVM nightly on Travis
Added new test WriteTest::testEmptyIdentityInsert().
Merge pull request #524 from josemalonsom/add-test-empty-identity-insert

Added new test WriteTest::testEmptyIdentityInsert().
Tried fixing the HHVM installation again
Merge pull request #574 from stof/patch-1

Fixed the installation of HHVM nightly on Travis