tests/test-simplemerge.py.out

revset: remove order information from tree (API)

Keeping `order` in tree makes AST operation harder. And there could be
invalid cases if trees could be generated and compounded freely, like:

  SetA(order=define) & SetB(order=define)
                                  ^^^^^^ couldn't be satisfied

This patch changes the code to calculate order on the fly, during tree
traversal. Optimization of reordering `and` arguments is preserved by
introducing a new internal operation `flipand`.

.. api::

   revset.stringset() now takes 'order' as the last argument.

Differential Revision: https://phab.mercurial-scm.org/D451

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