revset: extend sorting tests

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extra : rebase_source : 548d745e951457aaa55da7f2e529fbc50f6113ac
extra : amend_source : 9e5ee8ed75b6c14acd85778201225cdc3b85d835
revset: added documentation and comment for spanset class

--HG--
extra : rebase_source : 65d7568249b597845bc93650552c008c25810da1
revset: add some documentation for lazyset

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extra : rebase_source : 59a6139190317a9438e1120edc4181e280ae11b2
revset: add documentation and comment for _generatorset

(clean up some old irrelevant comment in the process)

--HG--
extra : rebase_source : 6e3ca089f37089f5b1def94d84a91aec7b3b2c86