diagnostics: no longer include the yacc category in -Wall

It would be a pity to warn the users against Bison features...
http://lists.gnu.org/archive/html/bison-patches/2013-02/msg00107.html

* src/complain.h, src/complain.c (Wall): Disable Wyacc.
(Weverything): New (hidden so far) category which really denotes all
the categories (what used to be Wall).
(warnings_args, warnings_types): Adjust.
(warning_argmatch): Now !none = Weverything and conversely, no longer Wall.
* NEWS, doc/bison.texi, src/getargs.c: Adjust the documentation.
* tests/input.at (-Werror is not affected by -Wnone and -Wall): Adjust
by not using a -Wyacc type of warning.

NEWS

@@ -216,6 +216,11 @@ GNU Bison NEWS
     bar.y: error: shift/reduce conflicts: 1 found, 0 expected
     bar.y: error: reduce/reduce conflicts: 2 found, 0 expected
 
+** Incompatibilities with POSIX Yacc
+
+  The 'yacc' category is no longer part of '-Wall', enable it explicitly
+  with '-Wyacc'.
+
 ** Additional yylex/yyparse arguments
 
   The new directive %param declares additional arguments to both yylex and