changed the returned value of width()/height() back to a number.

**Note: this may not a bug, but I think there is a better solution to handle the unity thing.**
### solution decription
there was [a older commit](https://github.com/01org/appframework/commit/a94fdadcb39e64dd7e5d4164384ad4e36bf2bdc5) from kyo-ago, I did not figure out why such a change has been made, after modification, the users who are familiar with jQuery will be strongly confused, and didn't see any benefit from that change.
Here is the [issue](https://github.com/01org/appframework/issues/483).

### how to do it better?
just convert the variable `tmpVal` from string to number via `+tmpVal`, so only number will be returned from `width()/height()` now, everybody's happy.
Merge pull request #494 from LeoYuan/patch-2

changed the returned value of width()/height() back to a number.