Problem: exporting to a CSV file fails when using python3

Repeat by:
Install roundup using python3.
  * Bring up a tracker,
  * click 'home' unless already there,
  * click 'Download as CSV'

Error description:
  TypeError: byte string value expected, value of type str found

Location of failure:
  write method of the Writer class in roundup/cgi/wsgi_handler.py

Cause of error:
  Python3 expects the argument to the write method to be a byte string
(e.g. b'somestring') where python 2.7 expects a string.

Solution:
Change the write method to convert the string using the encode function
for utf-8. In python 2.7 this encode function returns a string which is
== to the argument. In python 3 it returns a byte string. The attached
hg diff file contains the details.

Existing practice in the Roundup code for such cases (converting something 
that in Python 3 might be a str or bytes object to bytes) is to use bs2b 
(from roundup.anypy.strings).

Thanks for the review Joseph. I attached the updated diff.

Of course I tested it to make sure it still works.

Thanks, I've committed this patch.

fixed it in the CSV action now (as the issue wasn't limited to the WSGI 
interface), commit f74d078cfd9a