Load Pickle in the VM module in VM.getPort and VM.new.

* So it is only loaded when we are about to need it
  (we cannot easily load it in Send).
* If someone uses a reference to VM.getPort, then passing it around
  carries the dependency on Pickle, which is necessary.
* Messages sent to monitor streams are fine as they do not need Pickle.
Merge pull request #190 from eregon/mvm

Load Pickle in the VM module in VM.getPort and VM.new.