some simplistic transitive reduction, couple of basic tests, and getting
rid of the non-subsumption checking visitor in favor of more generic
checker which takes arbitrary conditions. 
(correctness of transitive reduction isn't yet tested on complex inputs,
e.g., SEP).
Merge branch 'alc' of https://github.com/klinovp/elk.git into alc
Another set of fixes (and some simplification) for the transitivity
encoding in the presence of hierarchies. More tests.