more fiddling with Sledgehammer's "add:" option

beta eta contract the Sledgehammer conjecture (and also the axioms, although this might not be needed), just like Metis does (implicitly); another consequence of the transition to FOF

generalize the "too general equality" code to handle facts like "x ~= A ==> x = B"

encode "fequal" reasoning rules in Metis problem, just as is done for Sledgehammer -- otherwise any proof that relies on "fequal" found by Sledgehammer can't be reconstructed