* tests/python/ipnbdoctest.py: Adjust to Python <3.6.
* tests/python/_autparserr.ipynb: Adjust to older IPython version.
* tests/python/stutter-inv.ipynb: Avoid pandas because its output
varies from version to version.

* tests/python/_autparserr.ipynb: New files, containing error
checking code from automata-io.ipynb and piperead.ipynb.
* tests/python/automata-io.ipynb: Remove error checks, and pipe
examples from piperead.ipynb.
* tests/python/piperead.ipynb: Delete.
* tests/python/word.ipynb: Move error checking code...
* tests/python/_word.ipynb: ... in this new file.
* doc/org/tut.org, tests/Makefile.am: Adjust.