[Buildbot] #3435: Install docs dependencies in setup.py

[Buildbot trac]

#3435: Install docs dependencies in setup.py
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Reporter:  dustin     |      Owner:  dustin
    Type:  undecided  |     Status:  new
Priority:  minor      |  Milestone:  0.9.+
 Version:             |   Keywords:
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 The docs makefile currently runs `pip install` for a bunch of dists, which
 probably surprises people (it surprised me!).

 Instead, we can install these as as feature in setup.py (so, `pip install
 buildbot[docs]`).  I'll adjust the Makefile to fail clearly if those dists
 aren't availeble, too.

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Ticket URL: <http://trac.buildbot.net/ticket/3435>
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