extdiff: add a --patch argument for diffing changeset deltas One of the things I missed the most when transitioning from versioned MQ to evolve was the loss of being able to check that rebase conflicts were properly resolved by: $ hg ci --mq -m "before" $ hg rebase -s qbase -d tip $ hg bcompare --mq The old csets stay in the tree with evolve, but a straight diff includes all of the other changes that were pulled in, obscuring the code that was rebased. Diffing deltas can be confusing, but unless radical changes were made during the resolve, it is very clear when individual hunks are added, dropped or modified. Unlike the MQ technique, this can only compare a single pair of csets/patches at a time. Like the MQ method, this also highlights changes in the commit comment and other metadata. I originally tried monkey patching from the evolve extension, but that is too complicated given that it depends on the order the two different extensions are loaded. This functionality is also useful when comparing grafts however, so implementing it in the core is more than just convenience. The --change argument doesn't make much sense for this, but it isn't harmful so I didn't bother blocking it. The -I/-X options are ignored because of a limitation of cmdutil.export(). We'll fix that next.