Make EXIT and SIGNAL patterns a requirement in test specifications

This will make sure regression tests do not spuriously pass despite, e.g.,
failing an invariant.

Author: tautschnig

regression/test.pl

@@ -64,6 +64,8 @@ ($)
   close FILE;
 
   chomp @data;
+  grep { /^\^EXIT=[\(\|\d]*\d+\)?\$$/ } @data or die "$fname: Missing EXIT test\n";
+  grep { /^\^SIGNAL=\d+\$$/ } @data or die "$fname: Missing SIGNAL test\n";
   return @data;
 }