fread returns a size_t and can never be -1. fread can signal parameter errors on some platforms, but this isn't portable. Remove this check and break out of the loop when fread returns 0. ok op@

- fix compilation error with DEBUG 1, after moving patience state out of diff_atom, and after renaming diff_data.d to diff_data.root. - add some missing newlines. - also debug "HIT" on a max-effort cut, like when finding a mid snake, which eases finding all the places where boxes get cut.