This moves out the concept of a "default VM" from the Environment class
and makes it the responsibility of the V1 configuration that at least
one VM is defined on it. This lets the configuration ultimately decide
what a "default" implementation is.
Previously, all procs were assumed to just be the current version. This
is certainly not going to be true always so now the version number of
the configuration must be explicit if you're assigning a proc to the
configuration loader.
Mitchell Hashimoto