Included waflib relies on deprecated "pipes" library

Here's some sort of advance warning. Python 3.13 drop the `pipes` library that is used in `waflib/extras/genpybind.py`.

This is courtesy of lintian that now tells me this:
```
I: hamster-time-tracker source: uses-deprecated-python-stdlib pipes (deprecated in Python 3.11, removed in Python 3.13) [waflib/extras/genpybind.py:2]
```

Not sure if there's a new waf release that gets rid of this.