add setFlip, getFlipX, getFlipY and tracking of flip state to Sprite.java
DOES consider negative coords in constructor
copy flipX,flipY in Sprite.set method
remove flip fields, rely on isFlipX/Y methods of TextureRegion parent
Merge pull request #1207 from jrenner/sprite

add setFlip, getFlipX, getFlipY and tracking of flip state to Sprite.java