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).

roundup.anypy package - Python version compatibility layer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Roundup currently supports Python 2.3 to 2.6; however, some modules
have been introduced, while others have been deprecated.  The modules
in this package provide the functionalities which are used by Roundup

- adapting the most recent Python usage
- using new built-in functionality
- avoiding deprecation warnings

Use the modules in this package to preserve Roundup's compatibility.

# vim: si