hgk: don't honor whitespace and format-changing diffopts
The diff-tree command is a plumbing command in Git, which means it is expected
to have a stable output format. Ensure that our output is stable too.
patchbomb: don't honor whitespace and format-changing diffopts (BC)
The whitespace diffopts break lossless transmission, and the format-changing
ones make import harder. We expect parsers to be able to read git-style diffs,
though.