make writeln a C built-in.

os/pl-file.c

@@ -5877,6 +5877,7 @@ static const PL_extension foreigns[] = {
   FRG("write",			1, pl_write,		      ISO),
   FRG("writeq",			1, pl_writeq,		      ISO),
   FRG("print",			1, pl_print,			0),
+  FRG("writeln",		1, pl_writeln,			0),
   FRG("nl",			1, pl_nl1,		      ISO),
   FRG("format",			2, pl_format,		     META),
 

pl/yio.yap

@@ -58,8 +58,7 @@ setting and clearing this flag are given under 7.7.
         ttynl/0,
         ttyput/1,
         ttyskip/1,
-        write_depth/2,
-        writeln/1], ['$default_expand'/1,
+        write_depth/2], ['$default_expand'/1,
         '$extend_file_search_path'/1,
         '$set_default_expand'/1]).
 
@@ -322,17 +321,6 @@ Like display/1, but using stream  _S_ to display the term.
 display(Stream, T) :-
 	   write_term(Term, T, [ignore_ops(true)]).
 
-/** @pred  writeln( _T_) is iso 
-
-
-Same as write/1 followed by nl/0.
-
- 
-*/
-writeln(T) :-
-	write(T),
-	nl.
-
 /* interface to user portray	*/
 '$portray'(T) :-
 	\+ '$undefined'(portray(_),user),