Renamed slot holding type expanders.
Removed slot for setf expanders, now in the function-entry.
Added a SETF-EXPANDER slot to the FUNCTION-ENTRY class.
Clarify that FMAKUNBOUND removes any SETF expander.
FMAKUNBOUND now removes the SETF expander.
Method on SICL-ENV:SETF-EXPANDER.
Method on (SETF SICL-ENV:SETF-EXPANDER).