updated some sledgehammer proofs -- much faster;

updated sledgehammer proof after breakdown of metis (exception Type.TUNIFY);

recovered type matching, which was broken in 8a765db7e0f8 (see also 8a765db7e0f8, 2db1d3d2ed54); NB: "match" operates on direct substitution without variable chasing, in contrast to "unify" (and Unify.matches!) which work on cascaded env;