Bug#664542: Workaround - create a separate 'changelog_opener'

[Dominique Brazziel]

	The basic idea is to create a second 'changelog opener'
in the same place in which the opener including proxy_support 
is created (UpdateManager/Frontend/Gtk/utils.py):

    # Create a changelog URL opener
    LOG.debug("Creating changelog URL opener.")
    changelog_opener = urllib2.build_opener()

then reference
that opener in method '_do_fetch' of
UpdateManager/DistSpecific/changelog.py:

     # changelog_opener support
     from UpdateManager.Frontend.Gtk.utils import init_proxy
     ...
     #connection = urllib2.urlopen(url)
     connection = changelog_opener.open(url)