Code review comment for lp:~mhr3/dee/add-changesets

Great stuff, looks good, some suggestions though:

1) I think it would make sense to implement a rudimentary check for dee_model_begin_changeset / dee_model_end_changeset calls to ensure they're called in a sequence, e.g. by maintaining an internal flag, so that calling end/begin or begin/begin etc. would give a warning.

2) Can you extend the tests to check that "started" signal arrives before "end"?