tox: tweak configuration

Fix the `list_dependencies_command` so arguably the most important
packages are not hidden (pip, setuptools, and wheel).

tox.ini

@@ -14,7 +14,7 @@ deps=-rtests/requirements.txt
 # from being added to `sys.path`.
 install_command=python -c 'import sys; sys.path.remove(""); from pkg_resources import load_entry_point; load_entry_point("pip", "console_scripts", "pip")()' install {opts} {packages}
 # Same as above.
-list_dependencies_command={envbindir}/pip freeze
+list_dependencies_command={envbindir}/pip freeze --all
 setenv=COVERAGE_FILE={toxworkdir}/.coverage.{envname}
 # TODO: The passed environment variables came from copying other tox.ini files
 # These should probably be individually annotated to explain what needs them.