bdiff: fix yet more fallout from xdiff long/int64 conversion (
issue5885)
"l" in Py_BuildValue's format string means long, so passing int64_t
instead results in fireworks on 32bit architectures.
Differential Revision: https://phab.mercurial-scm.org/D3538
shortest: avoid magic number "41"
As suggested by Yuya. Feel free to fold into D3502.
Differential Revision: https://phab.mercurial-scm.org/D3531