Animation does not work on Safari 6

[vicb]

Animation unit tests fails on Safari 6:

Safari 6.0.5 (Mac OS X 10.8.4) CssAnimation should correctly respond to an animation lifecycle FAILED
    Test failed: Caught Expected: <true>
      Actual: <false>
     Expected div to have css class "remove-end"

The tests are fine with Safari 7.
#1288 adds the "SL_Safari6" browser to the karma config. It could be used to launch the tests on SauceLabs.

Once this issue is solved, Safari 6 tests should be re-enabled

[vicb]

fixed by #1410