Center anchored actors are not drawn at correct canvas coords when scaled

[kamranayub]

Steps to Reproduce

1. Create an Actor (0, 0, 10, 10)
2. Scale the Actor by 2x
3. Set Actor.anchor to 0.5
4. Add Actor to game

Expected Result

When drawn, Actor should be twice as big (20x20) centered on (0, 0)

Actual Result

Actor is drawn at proper scale but off-center as shown here:

The Green square is a 2x actor centered on (0, 0) and should perfectly contain the red and blue squares.

Environment

• browser: Chrome
• browser version: 51
• operating system: Windows 10 x64

[kamranayub]

I added a new visual test for testing anchoring with fillRect and Sprite drawing. It's a mess in the current version, as you can see:

The anchor is being double-scaled and sprite drawing is super weird even with setCenterDrawing to false for everything except the center test.

After making some changes to the draw call logic, I believe I've fixed it properly:

I removed all the center drawing cruft, since now it will properly draw anchored correctly.

I'll submit a PR with the change.