Pcbnew: make block rotate honor the rotation angle setting. (fixes lp:1281605)

* Make block rotate command honor the rotation angle setting.  Thank you
  Umesh Mohan <mohan.umesh@gmail.com> for the patch.
* Change block rotate undo command from UR_ROTATE to UR_CHANGED so consecutive
  rotations do not lead to round errors and for proper undo in case the user
  changes the rotation angle setting between block rotations.