Fix behavior of AnimationSet and fillBefore

The previous logic in AnimationSet when starting an animation
ignored the fillBefore behavior of its child animations. This caused
a bug where a delayed AlphaAnimation would automatically cause the
target view to become transparent, even though it was supposed to wait
until after some delay to do so.
The fix checks the fillBefore behavior of each child animation before
concatenating its transform with the transform of the AnimationSet.

Change-Id: I76a2dafbe6dd338dc5281b17612eae87af168d86