tests: use assert instead of plain abort.

* tests/actions.at, tests/calc.at, tests/conflicts.at,
* tests/cxx-type.at, tests/glr-regression.at, tests/input.at,
* tests/named-refs.at, tests/regression.at, tests/torture.at,
* tests/local.at:
Prefer assert to abort.

tests/conflicts.at

@@ -57,6 +57,7 @@ AT_DATA_GRAMMAR([input.y],
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <assert.h>
 
 #define YYERROR_VERBOSE 1
 ]AT_YYERROR_DEFINE[
@@ -67,8 +68,7 @@ static int
 yylex (void)
 {
   static size_t toknum;
-  if (! (toknum <= strlen (input)))
-    abort ();
+  assert (toknum <= strlen (input));
   return input[toknum++];
 }