Comment 6 for bug 728751

well its disputed: http://en.wikipedia.org/wiki/Serial_comma

its probably better to reformat the message instead, e.g:
>sponsor-patch: Error: Unsupported builder specified: gsgs.
>sponsor-patch: Error: Supported builders: cowbuilder, cowbuilder-dist, pbuilder, pbuilder-dist, sbuild

maybe also get rid of the long if clause in get_builder too?
e.g. like this:

    supported = {
      "cowbuilder": lambda: Pbuilder("cowbuilder"),
      "cowbuilder-dist": lambda: Pbuilderdist("cowbuilderdist"),
      "pbuilder": lambda: Pbuilder(),
      "pbuilder-dist": lambda: Pbuilderdist(),
      "sbuild": lambda: Sbuild()
    }
    if builder in supported:
      return supported[builder]()

    Logger.error("Unsupported builder specified: %s." % builder)
    Logger.error("Supported builders: %s" % ", ".join(sorted(supported.keys())))