Fix missing API docs
Use goog.math.toDegrees
Add missing jsdoc tag
Only update rotate control element when it's needed

To avoid a lot of 'Recalculate style' events by the browser.
Remove unnecessary local variable
Merge pull request #2571 from fredj/rotatecontrol-cleanup

ol.control.Rotate cleanup and optimization
Restore opacity after drawing vector layers
Merge pull request #2509 from probins/apimismatch

Fix missing API docs
Merge pull request #2575 from tonio/vectoropacity

Restore opacity after drawing vector layers