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
Stage3D : remove Vector.ofArray as no more needed + fix bug on multiple indexBuffer draw call
Stage3d: oups, forgot that Flash still need Vector.ofArray (thanks Andy)
Added "allow trans" flag to SimpleSurface

Internally, SimpleSurface may or may not have alpha. Depending on how the
surface was loaded or whether you have tried to perform an operation that
requires alpha, it will update automatically. This is a good balance for
performance and memory.

Now, the "allow trans" flag will mask incoming "setPixel" and "setPixels"
calls on the when the surface is supposed to remain opaque.

This should fix operations such as:

var bitmapData = new BitmapData (100, 100, false);
bitmapData.setPixel32 (0, 0, 0x00FFFFFF);
trace (bitmapData.getPixel32 (0, 0));