[CSS21] Section C.4.21 is bogus

Section C.4.21 of CSS2.1 says:

   Clarification to the following lines:

     The :before and :after pseudo-elements elements allow values
     of the 'display' property as follows:

     ....

What the spec _actually_ changes from CSS2 at this point is remove this text 
completely, and furthermore remove the "User agents must ignore the following 
properties with :before and :after pseudo-elements: 'position', 'float', list 
properties, and table properties" text.  The changes list should be updated 
accordingly.

-Boris