Fix problem trying to prune a reaction that's not in the edge.

(Presumably it was in the core??)
Use DFT_QCI_thermo database before comparing thermo estimates.
Refactor the chemkin importer code.

Move the "check reactions" into a separate function,
and now we can put it inside a while loop, so that if one set
of matches invalidates some reactions they are re-checked
immediately.