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/getargs.c

@@ -59,7 +59,7 @@ bool glr_parser = false;
 
 int report_flag = report_none;
 int trace_flag = trace_none;
-int warnings_flag = warnings_none;
+int warnings_flag = warnings_other;
 
 static struct bison_language const valid_languages[] = {
   { "c", "c-skel.m4", ".c", ".h", true },
@@ -230,6 +230,7 @@ static const char * const warnings_args[] =
   "none            - no warnings",
   "midrule-values  - unset or unused midrule values",
   "yacc            - incompatibilities with POSIX Yacc",
+  "other           - all other warnings",
   "all             - all of the above",
   "error           - warnings are errors",
   0
@@ -240,6 +241,7 @@ static const int warnings_types[] =
   warnings_none,
   warnings_midrule_values,
   warnings_yacc,
+  warnings_other,
   warnings_all,
   warnings_error
 };
@@ -330,6 +332,7 @@ Output:\n\
 Warning categories include:\n\
   `midrule-values'  unset or unused midrule values\n\
   `yacc'            incompatibilities with POSIX Yacc\n\
+  `other'           all other warnings (enabled by default)\n\
   `all'             all the warnings\n\
   `no-CATEGORY'     turn off warnings in CATEGORY\n\
   `none'            turn off all the warnings\n\