diffopts: notice a negated boolean flag in diffopts This means that if you have git-diffs enabled by default (pretty common) and you hit the rare (but real) case where a git-diff breaks patch(1) or some other tool, you can easily disable it by just specifying --no-git on the command line. I feel a little bad about the isinstance() check, but some values in diffopts are not booleans and so we need to preserve false iff the flag is a boolean flag: failing to do this means we end up with empty string defaults for flags clobbering meaningful values from the [diff] section in hgrc.