Perl error handler recognizes errors thrown from the C library.

test/travis.pl

@@ -181,7 +181,7 @@ eval
 or do
 {
     # If a backrest exception then return the code
-    exit $EVAL_ERROR->code() if (isException($EVAL_ERROR));
+    exit $EVAL_ERROR->code() if (isException(\$EVAL_ERROR));
 
     # Else output the unhandled error
     print $EVAL_ERROR;