Makes using shouldExpand with uneven tabs work correctly

With current implementation using shouldExpand="true" with tabs that aren't of the same width may result in cropping longer tab labels. 


This is due to setting  
```java
new LinearLayout.LayoutParams(0, LayoutParams.MATCH_PARENT, 1.0f)
```
layout params for every tab whenever the tabs are expanded to fill the whole screen width.


This fix gets weight from the width of the tab: 
```java
new LinearLayout.LayoutParams(0, LayoutParams.MATCH_PARENT, tabView.getMeasuredWidth())
```
during the fitting. Thanks to that, the tabs retain their previous proportions.

# Current behaviour:
![before](https://f.cloud.github.com/assets/721925/1407219/b773745a-3d66-11e3-896d-fa09a350dd0e.png)

# After applying this fix:
![after](https://f.cloud.github.com/assets/721925/1407218/b75c126a-3d66-11e3-9994-4857ac9cfcd1.png)