Fixes for compatibility with Emacs 26.1.

pure-mode.el:2273:31:Error: Duplicate &optional

https://github.com/agraef/pure-lang/commit/717fd7af516ce5bb83a7da2c869a55fde41018b8
--- etc/pure-mode.el.orig
+++ etc/pure-mode.el
@@ -2270,7 +2270,7 @@ If prefix ARG is not nil, remove an existing tracepoint instead."
 	   (indent-to (eval (cdr indent-fun)))
 	   ))))
 
-(defun pure-alignment-column (&optional lim &optional flag)
+(defun pure-alignment-column (&optional lim flag)
   "Look for an alignment column (`=') in the vicinity of
 point. LIM, if given, limits the search to the region between
 point and LIM. Return a list of two elements: (EQUALS-COL