merge: replace a repo.lookup('.') by more typical repo['.'].node()
The `repo.lookup('.')` form comes from b3311e26f94f (merge: fix
--preview to show all nodes that will be merged (issue2043).,
2010-02-15). I don't know why that commit changed from `repo['.']`,
but I don't think there's any reason to do that. Note that performance
should not be a reason (anymore?), because repo.lookup() is
implemented by first creating a context object.
Differential Revision: https://phab.mercurial-scm.org/D7998
wrap 0: [0, 'orig']
wrap 1: [1, 0, 'orig']
wrap 2: [2, 1, 0, 'orig']
wrap 3: [3, 2, 1, 0, 'orig']
wrap 4: [4, 3, 2, 1, 0, 'orig']
wrap 0: [0, 4, 3, 2, 1, 0, 'orig']
unwrap 3: 3: [0, 4, 2, 1, 0, 'orig']
unwrap -: 0: [4, 2, 1, 0, 'orig']
unwrap 0: 0: [4, 2, 1, 'orig']
unwrap 4: 4: [2, 1, 'orig']
unwrap 0: -: ValueError
unwrap 2: 2: [1, 'orig']
unwrap 1: 1: ['orig']
unwrap -: -: IndexError
context manager ['orig']
context manager [1, 'orig']
context manager [0, 1, 'orig']
context manager [2, 0, 1, 'orig']
context manager [2, 1, 'orig']
context manager [2, 'orig']
wrap callable object [0, 'orig']