Add another diagnostic to RegExpDag

Count labelled nodes under non-labelled roots. This number should come out to
be zero.
Nwpds: Use non-linearzed equations in SCCs with only one function

This introduces both tensored and non-tensored weights at the same time in the
system and the associated complications.
When using mixed weights in Nwpds, introduce two output modes.

Depending on some internal heuristic, Nwpds::poststar can return either
tensored or non-tensored weights on the output automaton. This heuristic
currently is -- always return tensored weights.
Use Fwpds::isOutputTensored to find the mode of weights on the output
automaton.
Merge branch 'nwpdsMixed' into nwpdsExperimental