Add ZeroMQ version to debug string.
ChildProcess should have a default empty impl of #run_process.
Another log message improvement.
Improve temp directory management.

Now uses the OS temp directory area, which makes it possible to run
specs out of a Vagrant mapped directory. (Previously, temp directories
were located underneath the checkout, which in Vagrant is usually a
network-mapped directory, so IPC creation doesn't work and zeromq fails
silently.)