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.

branching: merge with stable

builddependencies: don't remove found deps when divergence found (issue5946) It seems obviously wrong to not keep any dependencies for a revision that we had already found (for p1) if we run into divergence (from p2). It also happens to fix issue5946 :)

builddependencies: don't add dependency on revision outside input set This was already handled in the single-successor case, but had been missed in the multiple-successors case. Note that there seems to be a copy of builddependencies() in the topics extension. I don't use topics more than I have to, so I'll let someone else fix that code.

builddependencies: consider all divergent successors We were only considering one. In test-evolve-abort-conentdiv.t:165, the input revs were {5, 8} and dependency dict was {8: set([]), 5: set([10])}, which is a little weird (10 is not in the input set). It still worked because the callers used it (they seemed to only care if there were *any* dependencies). This patch fixes the issue by considering all successors. That means the dependency dict will be {8: set([]), 5: set([8, 10])} after this patch. The next patch will remove the 10 from that set.