prove_case_equation now calls uses meta_eq_to_obj_eq to cope with new form of 'split'. Tried calling simp_tac instead of using resolution with trans, but it was significantly slower: 98.3 secs instead of 91.2 secs for ex/Enum.

show_sorts:=true forces display of types

trivial rewording

trivial change

Covers wrapper tacticals: setwrapper, ..., addss

fixed bug in thy_unchanged that occurred when the .thy file was changed but the .ML file hadn't been read before; tmpfile is now deleted immediatly after reading the .thy file in use_thy