Port to GCC 2.95. First two problems reported by Michael Deutschmann in

<http://lists.gnu.org/archive/html/bug-bison/2006-09/msg00018.html>.

* src/parse-gram.y (symbol_declaration): Don't put statements
before declarations; it's not portable to C89.
* src/scan-code.l (handle_action_at): Likewise.

* src/scan-code.l: Always initialize braces_level; the old code
left it uninitialized and therefore had undefined behavior.

Don't attempt to redefine 'assert', since it runs afoul of
systems where standard headers (mistakenly) include <assert.h>.
Instead, define and use our own alternative, called 'aver'.
* src/reader.c: Don't include assert.h, since we no longer
use assert.
* src/scan-code.l: Likewise.
* src/system.h (assert): Remove, replacing with....
(aver): New function, taking a bool arg.  All uses changed.
* src/tables.c (pack_vector): Ensure that aver arg is bool,
not merely an integer.

src/output.c

@@ -235,7 +235,7 @@ prepare_rules (void)
       /* Merger-function index (GLR).  */
       merger[r] = rules[r].merger;
     }
-  assert (i == nritems);
+  aver (i == nritems);
 
   muscle_insert_item_number_table ("rhs", rhs, ritem[0], 1, nritems);
   muscle_insert_unsigned_int_table ("prhs", prhs, 0, 0, nrules);
@@ -342,7 +342,7 @@ token_definitions_output (FILE *out)
       /* At this stage, if there are literal aliases, they are part of
 	 SYMBOLS, so we should not find symbols which are the aliases
 	 here.  */
-      assert (number != USER_NUMBER_ALIAS);
+      aver (number != USER_NUMBER_ALIAS);
 
       /* Skip error token.  */
       if (sym == errtoken)