This is a breaking API change (not that we care about that at this point). This can avoid redundant work spent on atomizing a file multiple times. There are use cases where one particular file must be compared to other files over and over again, such as when blaming file history. The old API gave access to both versions of the file to the atomizer just in case a future atomizer implementation needs this. This can still be achieved by passing a second file via the atomizer's private data pointer.

- 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.