Patch #37274: Circle select for node editor, by Henrik Aarnio (hjaarnio).

Circle select was missing from node editor, and C key was assigned to now defunct "show cyclic dependencies". This patch remaps the key and adds circle select operator.
Functions to check intersection between rctf/rcti and a circle were also added to rct.c for code cleanliness and consistency.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@61173 954f8c5b-7b00-dc11-b283-0030488c597c