Fix RTL callouts: flip left/right and reverse x adjustment

LTR:
<img src='https://cloud.githubusercontent.com/assets/413693/5352072/8e10cdce-7f14-11e4-9994-b356ff4124f8.png' width='400'>

RTL before:
<img src='https://cloud.githubusercontent.com/assets/413693/5352074/8ed27f64-7f14-11e4-8000-c654d813da8d.png' width='400'>

RTL after:
<img src='https://cloud.githubusercontent.com/assets/413693/5352076/8ffe389c-7f14-11e4-8ce5-3ef93521f6c5.png' width='400'>