UI small fixes:

- Theme color for the brush popup was not correctly coded. Now it follows menu item
  style correctly, which also allows all the themes we have to give readable text.

- RMB cancel also added for slider buttons and the color picker.



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55553 954f8c5b-7b00-dc11-b283-0030488c597c