This completes the changes required for #221.

Adjusts for the fact that the old task.is_waiting() test used to return
True for retrying tasks as well as ones in the 'waiting' state. Now we
do direct tests on the state value, so must check for 'retrying' too
where appropriate.
Warn if internal queue members are not used in the graph.

This closes #214.
Closes #44: disallow declaring families to be sequential.
Deleted obsolete comment.
Added .tex sources as deps in doc Makefile.

This allows re-make after changes to the source, without deleting the
generated documents.
Merge pull request #228 from hjoliver/doc-makefile-deps

Added .tex sources as deps in doc Makefile.
Merge pull request #225 from hjoliver/221-follow-up

This completes the changes required for #221.
Merge pull request #227 from hjoliver/44-sequential-families

Closes #44: disallow declaring families to be sequential.
Merge pull request #226 from hjoliver/214-queue-config-check

Warn if internal queue members are not used in the graph.