Process.cpu_affinity() should accept a set() (or other iterables)

[giampaolo]

~/svn/psutil {master}$ python -c "import psutil; psutil.Process().cpu_affinity(set([0]))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "psutil/__init__.py", line 702, in cpu_affinity
    self._proc.cpu_affinity_set(cpus)
  File "psutil/_pslinux.py", line 649, in wrapper
    return fun(self, *args, **kwargs)
  File "psutil/_pslinux.py", line 961, in cpu_affinity_set
    cext.proc_cpu_affinity_set(self.pid, cpus)
TypeError: sequence argument expected, got set

This is kind of related to #525. Since in #525 we're going to return a set it is better for cpu_affinity() (set) to also accept a set or any other iterable.

[giampaolo]

Fixed in 4320a32.