forwarder: Fix bug for data hop counter.

Credits to Alex.
ndn-face: Fix bug for data hop counter.

Credits to Alex.
zipf-mandelbrot: Adding hop counter.
ndn-consumer: Adding hop counter.
ndn-app-delay-tracer: Tracer added.
ndn-tree-app-delay-tracer: Example added.
wscript: Including newly added tracer.