Fix Python 3 issues in REST code. * Need to use .get not .getheader for HTTP headers (see hg commit fec18298ae02, "Python 3 preparation: HTTP headers handling in roundup_server.py."). * Need to use key not cmp with sort (see hg commit 3fa026621f69, "Python 3 preparation: comparisons."). * dispatch output must be bytes, not str, otherwise writing it to the socket (e.g. in roundup-server) will fail. This fixes issues shown up attempting to access the REST interface with a browser with Python 3 (as opposed to with the Roundup testsuite, which also has known REST issues with Python 3).

from roundup.dist.command.build import build_message_files, check_manifest
from distutils.command.install_lib import install_lib as base

class install_lib(base):

    def run(self):
        check_manifest()
        build_message_files(self)
        base.run(self)