Found via `codespell -q 3 --skip="*.po"`

https://github.com/NetworkManager/NetworkManager/pull/203

It's not an example and not actually used.

https://github.com/NetworkManager/NetworkManager/pull/141

This breaks client tests on avery old kernel (2.6.32, RHEL 6).

  Traceback (most recent call last):
    File "./clients/tests/test-client.py", line 699, in setUp
      self.srv = NMStubServer(self._testMethodName)
    File "./clients/tests/test-client.py", line 309, in __init__
      start = nmex.nm_boot_time_ns()
    File "/builddir/build/BUILD/NetworkManager-1.11.4/examples/python/nmex.py", line 54, in nm_boot_time_ns
      return sys_clock_gettime_ns(CLOCK_BOOTTIME)
    File "/builddir/build/BUILD/NetworkManager-1.11.4/examples/python/nmex.py", line 50, in sys_clock_gettime_ns
      return _sys_clock_gettime_ns(clock_id)
    File "/builddir/build/BUILD/NetworkManager-1.11.4/examples/python/nmex.py", line 39, in f
      raise OSError(errno_, os.strerror(errno_))
  OSError: [Errno 22] Invalid argument

This reverts commit 119e828dbeeeab134e83890b18d0b7a0c1838786.

According to the D-Bus API specification we return CLOCK_BOOTTIME only.
We don't support kernels too old to have it -- the fall back to
CLOCK_MONOTONIC is only there to be able to run unit tests on RHEL 6
kernel and will eventually go away.

The libnm API fir checkpoints was only introduced with 1.11. It
is not yet stable, so there is still time to adjust it. Note that
this changes API/ABI of the development branch.

Changes:

- we only add async variants of the checkpoint functions. I believe
  that synchronous D-Bus methods are fundamentally flawed, because
  they mess up the ordering of events.
  Rename the async functions by removing the "_async" suffix. This
  matches glib style, for which the async form is also not specially
  marked.

- for function that refere to a particular checkpoint (rollback and
  destroy), accept the D-Bus path as string, instead of an NMCheckpoint
  instance. This form is more flexible, because it allows to use
  the function without having a NMCheckpoint instance at hand. On the
  other hand, if one has a NMCheckpoint instance, he can trivially
  obtain the path to make the call.

- make python2 and python3 compatible
- support Checkpoint create flags (requires recent libnm for GI
  of flags)
- support adjust-rollback-timeout command
- print elapsed time in show output

We need common operations from the python scripts.
For example, to print the boot-time.

Move such utils to a separate nmex.py file ("ex" for
example). This file should contain helper functions that
are pure python (or, if the have requirements, load them
only on demand, so that examples that need those have
additional dependencies). It should also be simple to extract
individual helpers from nmex, so that the user can take an
example, merge parts of nmex.py in, and modify it to his needs.

Note that this changes API for checkpoint_create_async() in Python
via GIR. Previously it would require an integer argument, now a flags
argument. But this API is still unstable, it will be introduced with
1.12.