test-obsolete-rebase.t: test --abort and --continue

obsolete: handle rebase --collapse Recording obsolete in concludenode() did not work for --collapse because only the first revision was passed to the call. The new strategy is to track the rebase state in defineparents() and concludenode() and to create markers only after a successful non-abort call. In theory, this should also fix --continue/--abort cases. The change in test-stabilize-order.t comes from concludenode() no longer creating obsolete marker. stabilize command was actually duplicating markers, once in concludenode(), once explicitely.

test-stabilize-order.t: trace obsolete markers Will prevent breakage in rebase.concludenode() overriding.

test-obsolete-rebase.t: move --keep test from test-obsolete.t

obsolete: handle rebase removing empty changesets The new revision identifier returned by concludenode() was None and was not correctly translated to nullid.

obsolete: add or fix debug commands help

obsolete: do not duplicate command help

obsolete: use new-style command registration

obsolete: make rebase abort with --keep obsolete modifies rebase to mark rebased changesets obsolete instead of stripping them, which makes --keep irrelevant.

obsolete: fix rebase wrapping ui and repo arguments were swapped which made --keep calls traceback.