Proposal of add more sophisticated repository iterators

[lukaszb]

As a general idea, in git when You iterate the log, it shows You only log for current (e.g. master) branch. This is much different than what mercurial is showing.

My proposal is to add, 'getiterator(branch=None)' function that will generate iterator function for mercurial repository and will iterate only on revision for passed branch parameter. That would be a nice addition to next/prev functions of changeset.

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Reference: https://bitbucket.org/marcinkuzminski/vcs/issues/44/