cleanupnode: do not use generator for node mapping
The 'successors' part of the mappings used of be a tuple. This avoid issue from
code consuming the generator "by mistake". For example, an extension inspecting the
mapping content used to be able to iterate over the successors mapping without
consequence.
Since the mapping are small we do not expect any performance impact we use tuple
again for this.
$ hg init repo
$ cd repo
$ touch foo
$ hg ci -Am 'add foo'
adding foo
$ hg up -C null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
this should be stored as a delta against rev 0
$ echo foo bar baz > foo
$ hg ci -Am 'add foo again'
adding foo
created new head
$ hg debugindex foo
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 0 ..... 0 b80de5d13875 000000000000 000000000000 (re)
1 0 13 ..... 1 0376abec49b8 000000000000 000000000000 (re)
$ cd ..