Add -Wother so -Wnone suppresses all warnings.

Reported by George Neuner at
<http://lists.gnu.org/archive/html/bug-bison/2010-08/msg00002.html>.
* NEWS (2.5): Document.
* THANKS (George Neuner): Add.
* doc/bison.texinfo (Bison Options): Document.
* src/complain.c, src/complain.h
(warn_at, warn_at_indent, warn): Suppress warning if -Wno-other.
(midrule_value_at): New warning function, similar to yacc_at in
that it's controlled by its own warning category.
* src/getargs.c (warnings_flag): Initialize to warnings_other.
(warnings_args, warnings_types): Add entry for warnings_other.
(usage): Update.
* src/getargs.h (enum warnings): Add entry for warnings_other.
* src/gram.c (grammar_rules_useless_report): If -Wno-other, then
don't print useless rules.
* src/reader.c (symbol_should_be_used): Rather than adjusting the
return value based on whether midrule value warnings are enabled,
accept a new parameter for telling the caller whether true is
being returned for a potential midrule warning.
(grammar_rule_check): Use midrule_value_at for midrule value
warnings, and continue to use warn_at for all other warnings.  Let
them check whether the warnings are enabled.
* tests/local.at (AT_BISON_CHECK): Update documentation.
(AT_BISON_CHECK_NO_XML): Check that -Wnone and --warnings=none
disable all warnings exercised in the test suite.
(cherry picked from commit 8ffd7912e3)

src/complain.h

@@ -25,7 +25,8 @@
 extern "C" {
 # endif
 
-/** Informative messages, but we proceed.  */
+/** Informative messages, but we proceed.  Report iff
+    <tt>warnings_flag & warnings_other</tt>.  */
 
 void warn (char const *format, ...)
   __attribute__ ((__format__ (__printf__, 1, 2)));
@@ -61,6 +62,11 @@ void complain_at_indent (location loc, unsigned *indent,
 void yacc_at (location loc, char const *format, ...)
   __attribute__ ((__format__ (__printf__, 2, 3)));
 
+/** A midrule-value warning.  Report iff
+    <tt>warnings_flag & warnings_midrule_values</tt>.  */
+
+void midrule_value_at (location loc, char const *format, ...)
+  __attribute__ ((__format__ (__printf__, 2, 3)));
 
 /** A fatal error, causing immediate exit.  */