Signal C syscall in case of exception

[giampaolo]

This is aimed at those functions defined in C extension modules which internally calls multiple syscalls. Usually they fail with OSError or WindowsError. We have the error code and the message string but we don't know which syscall caused the error exactly. This is especially bad when receiving a bug report on Windows, since the single functions make invoke multiple syscalls. Instead of asking the user to debug the problem themselves we now pass a debug message string which produces an exception like this:

======================================================================
ERROR: psutil.tests.test_system.TestSystemAPIs.test_net_if_addrs
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Traceback (most recent call last):
  File "psutil/tests/test_system.py", line 582, in test_net_if_addrs
    nic_stats = psutil.net_if_stats()
  File "psutil/__init__.py", line 2288, in net_if_stats
    return _psplatform.net_if_stats()
  File "psutil/_pslinux.py", line 1034, in net_if_stats
    duplex, speed = cext.net_if_duplex_speed(name)
OSError: [Errno 25] Inappropriate ioctl for device (originated from ioctl(SIOCETHTOOL))

When we only exercise one syscall there's no need to add the additional information.
I did this for Linux, OSX, Windows and FreeBSD.