improved IE7 support

I know that we support IE8+ but now AA is unusable in IE7, see the screenshots.

![Screen Shot 2013-02-14 at 15 55 39](https://f.cloud.github.com/assets/153201/157141/020ed86e-76b7-11e2-9d7a-13e8adccdaed.png)

This patch makes heal AA from these pains in this legacy browser.

![Screen Shot 2013-02-14 at 15 55 29](https://f.cloud.github.com/assets/153201/157149/3bd2c3c6-76b7-11e2-9428-22b5c9bd043a.png)