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/system.h

@@ -136,6 +136,21 @@ typedef size_t uintptr_t;
 #include <stdbool.h>
 
 
+
+/*-------------.
+| Assertions.  |
+`-------------*/
+
+/* <assert.h>'s assertions are too heavyweight, and can be disabled
+   too easily, so use aver rather than assert.  */
+static inline void
+aver (bool assertion)
+{
+  if (! assertion)
+    abort ();
+}
+
+
 /*-----------.
 | Obstacks.  |
 `-----------*/
@@ -210,11 +225,6 @@ do {						\
 } while (0)
 
 
-/* Assertions.  <assert.h>'s assertions are too heavyweight, and can
-   be disabled too easily, so implement it separately here.  */
-#define assert(x) ((void) ((x) || (abort (), 0)))
-
-
 /*---------------------------------------------.
 | Debugging memory allocation (must be last).  |
 `---------------------------------------------*/