Vimproc via Vital.ProcessManager is not used correctly

[pyrho]

Several issues here:

1. On this line we check if the process state is existing. But Vital.ProcessManager never actually returns existing. According to this, state values are idle, inactive, reading and undefined. Not sure what this implies, but I would say it leads to some undefined behaviors.

2. Vital seems to have deprecated the ProcessManager API, maybe we should switch to the new API.