Process.parent() may swallow NoSuchProcess exceptions

[giampaolo]

...and return None instead. Problem is here:

psutil/psutil/__init__.py

Line 473 in 08964b0

if parent.create_time() <= self.create_time():

This is a race condition as the process may be alive at ppid = self.ppid() but not at self.create_time(). It's a very small time frame but the issues technically exists.