Changed the shouldExpand behavior to set the layout at the time the tab is added

On Android versions prior to 4.3 I observed a behavior in my app where the shouldExpand had no effect other than dropping the tabPadding. By moving the application of the expandedTabLayout instead of defaultTabLayout to the tab adding code as opposed to onMeasure code I was able to resolve the issue. The downside is that https://github.com/astuetz/PagerSlidingTabStrip/pull/42 is incompatible with this change as the weight can't be assigned beforehand.

See below for the illustration of the problem. With the fix both 4.0.3 and 4.3 behavior is the same for expansion.

![pagerslidingtabstrip-4 0 3](https://f.cloud.github.com/assets/1417338/1602476/abf02068-5398-11e3-8b74-8f323f7000db.png)
![pagerslidingtabstrip-4 3](https://f.cloud.github.com/assets/1417338/1602477/abfeafca-5398-11e3-9068-24cd7c92f8ad.png)