Fix a bottom scrollview content size mis-calculate bug. Not show horizon...

...tal scrollview indicator by default.

 It should not add a half container size to content size when buttons count equal to 2.
Horizontal scrollview indicator helps nothing when use finger to scroll the view. (hidden it)

Before:
![before](https://cloud.githubusercontent.com/assets/1056803/4179581/5e724b82-36cc-11e4-95ce-509a0fdee3b2.gif)

After:
![after](https://cloud.githubusercontent.com/assets/1056803/4179582/6175e71c-36cc-11e4-9b5d-4c7349be669d.gif)