使用scrollview后，alignParentBottom不起效，布局不能完全拉伸，match_parent无效
设置scrollView的fillViewPort属性为true
Romain Guy write a little info about a ScrollView attribute that is missing from documentation :android:fillViewport=”true” .
It must be set to ScrollView and has the following efect : when set to true, this attribute causes the scroll view’s child to expand to the height of the ScrollView if needed. When the child is taller than the ScrollView, the attribute has no effect.
原文：http://www.cnblogs.com/gyzboy/p/4618233.html