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).

#!/usr/bin/env python
from __future__ import print_function
import zlib, base64, sys
print(base64.encodestring(zlib.compress(sys.stdin.read())))