don't recurse infinitely in Data::Dumper

Add a configuration variable/option to limit recursion when dumping
deep data structures.

Defaults the limit to 1000, which can be reduced or increase, or
eliminated by setting it to 0.

This patch addresses CVE-2014-4330.  This bug was found and
reported by: LSE Leading Security Experts GmbH employee Markus
Vervier.