cleanup: use NotImplementedError instead of NotImplemented Caught by pyflakes.

CHANGELOG: add some entries and remove duplicated entries

branching: merge default into stable The stable branch of Mercurial core now contains Mercurial 4.7 so evolve branch policy requires this merge. The @ bookmark is in the right location, so people doing clone will get to the latest release.

branching: merge with the other head

test-compat: backed out changeset 8fe8152ff071 These output change were for 4.7 only.

test-compat: backed out changeset 41fc764bf28c These output change are for mercurial-4.7 only

test-compat: backed out changeset dda5b2134b32 These change were for Mercurial 4.7 only.

test-compat: backout change to 1e103c7f7663

compat: use older API for older version This API changed in 4.7, we need to adjust.

branching: create mercurial-4.6 branch for updated test output This branch will be used to check for 4.6 compatibility.

builddependencies: extract function for getting successors The code no longer makes a difference between single- and mult-successor cases and just needs a set (or generator, really) of successors to iterate over. Let's extract that into a function.

builddependencies: share code between single- and multi-successor cases The two cases now have more similar structure ("if succ in revs: dependencies[r].add(succ)"), so let's share the code so it doesn't start drifting apart again.

builddependencies: build inverse dict from forward dict It's error-prone to keep "dependencies" and "rdependencies" in sync (we don't do it correctly when there are multiple successors or a node). It's easier to just create "rependencies" from "dependencies" after it's complete.

builddependencies: remove a use of defaultdict I don't see much reason to make "rdependencies" be a defaultdict when "dependencies" is not. It's easy to initialize each entry ourselves.