Unit-test can now be run as for specific test and/or target.
Eg:
`haxe tools/unit-test/TestRunner.hxml && neko bin/nmetest.TestRunner.n nmetest.display.BitmapDataNMETest flash`
TravisCI: more progress on testing BitmapData
TravisCI: start xvfb with GLX extension
TravisCI: start xvfb manually
TravisCI: xvfb use 32-bit color depth
TravisCI: skip neko NME testes due to "Could not initialize SDL : No available video device"
Cpp tests are still running fine.
See https://travis-ci.org/andyli/NME/builds/6890558#L2225
Disable SWF dependency