Setting clone cursor is now an option for paint operator. This is not
too nice but it frees the Ctrl-LClick shortcut and allows us to set
invert mode for other paint tools, such as sharpen vs blur or invert
colour for draw brush. This conflict has existed on GSOC branch, better
resolve now before merging invert functionality.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55348 954f8c5b-7b00-dc11-b283-0030488c597c