Exim - CSA functions:

Code from CVS, but it applies to 4.50

      xim-csa.patch: <"http://www.cus.cam.ac.uk/%7Efanf2/hermes/doc/antiforgery/exim-csa.patch>
      
	  exim-csa.docs: <"http://www.cus.cam.ac.uk/%7Efanf2/hermes/doc/antiforgery/exim-csa.docs>