fix use of defpurefun

A defpurefun selector function was being declared in the top-level
module, and which used qualified names to access columns directly in the
bin module.  This should have actually been reported as a syntax error.
Instead, defun should be used and this changes it accordingly.

bin/lookups/bin_into_binreftable.lisp

@@ -1,4 +1,4 @@
-(defpurefun (selector-bin-to-binreftable)
+(defun (selector-bin-to-binreftable)
   (+ bin.IS_AND bin.IS_OR bin.IS_XOR bin.IS_NOT))
 
 (deflookup