CSS: Re-allow setting shorthand properties in IE<9

```
   raw     gz Sizes
284202  84383 dist/jquery.js
 96537  33455 dist/jquery.min.js

   raw     gz Compared to 1.x-master @ f361f0378b80f6141e79d906821f6964bcdfbfc4
  +123    +42 dist/jquery.js
    +7     +3 dist/jquery.min.js
```