Comment 6 for bug 1438865

While we've worked around this by setting RELEASE_UPGRADER_NO_SCREEN=1 in friendly-recovery, it'd be better to make sure that the screenrc file is loaded by the release-upgrader all the time.

So in DistUpgrade/DistUpgradeMain.py we should change how screenrc is loaded:

    # unset escape key to avoid confusing people who are not used to
    # screen. people who already run screen will not be affected by this
    # unset escape key with -e, enable log with -L, set name with -S
    cmd = ["screen",
           "-e", "\\0\\0",
           "-L",
           "-c", "screenrc",
           "-S", SCREENNAME]+sys.argv
    logging.info("re-exec inside screen: '%s'" % cmd)
    os.execv("/usr/bin/screen", cmd)