bdiff: use ssize_t in favor of Py_ssize_t in cpython-unaware locations This function and struct will be exposed via cffi, so we need to remove the cpython API dependency they currently have.

hgweb: enumerate lines in loop header, not before Doing this will allow access to the lines in arbitrary order (because the result of enumerate() is an iterator), and that will help calculating rowspan for annotate blocks.