"examples/python/gi/checkpoint.py" is not only an example. It's also a
useful script for testing checkpoints.
Support a "--last" argument to specify the last checkpoint created.
Otherwise, when you are using this example from a test script, it
can be cumbersome to find the right checkpoint point.
Also, rename "client" and "nm_client" variables to "nmc". The purpose of
using the same variable name for the same thing is readability, but also
it works better when copy+paste snippets into the Python REPL.
4d70c9c4db