[Buildbot] #3262: Missing dependencies for buildbot.manhole are reported poorly

[Buildbot trac]

#3262: Missing dependencies for buildbot.manhole are reported poorly
--------------------+-----------------------
Reporter:  exarkun  |      Owner:
    Type:  defect   |     Status:  new
Priority:  major    |  Milestone:  undecided
 Version:  0.8.10   |   Keywords:
--------------------+-----------------------
 Try to use `buildbot.manhole` without installing all of the dependencies
 for Twisted Conch and this happens:

 {{{
  File "/srv/buildmaster/config.py", line 46, in <module>
     maybeAddManhole(c, privateData)
   File "/srv/buildmaster/config.py", line 44, in maybeAddManhole
     c['manhole'] = AuthorizedKeysManhole(manhole['port'],
 authorized_keys.name)
   File "/usr/lib/python2.7/site-packages/buildbot/manhole.py", line 289,
 in __init__
     c = AuthorizedKeysChecker(keyfile)
 exceptions.NameError: global name 'AuthorizedKeysChecker' is not defined
 }}}

 which is unhelpful in figuring out which dependencies are missing and also
 makes the problem look like a really embarassing buildbot bug instead of a
 missing dependency.

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Ticket URL: <http://trac.buildbot.net/ticket/3262>
Buildbot <http://buildbot.net/>
Buildbot: build/test automation