rebase: clarify naming of variables holding node hashes - don't call them rev

bookmarks: factor out bookmark file opening for easier extensibility

merge with stable

diff: explicitly honor all diffopts 'hg diff' should naturally honor all diffopts.

annotate: explicitly only honor whitespace diffopts The whitespace ones are the only ones the annotate logic cares about anyway, so there's no visible impact.

notify: explicitly honor all diffopts The notify output doesn't seem to be parseable anyway, what with the maxdiff config option. Plus it is designed mainly for servers where hopefully the admins are doing sensible things.

jsonchangeset: don't honor whitespace and format-changing diffopts JSON is meant to be parsed by computers, and format changes can break them.

transplant: don't honor whitespace and format-changing diffopts transplant uses diff purely internally.

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.