progress: enforce use of complete() on the helper class
complete() is preferred over update(None), so let's enforce that.
Differential Revision: https://phab.mercurial-scm.org/D3822
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
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$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
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