Username configuration directive for knife rackspace reported incorrectly

When running `knife rackspace server list` with no configuration set I get this:

/usr/lib/ruby/gems/1.8/gems/fog-0.2.14/lib/fog/service.rb:20:in `new': rackspace_api_key and rackspace_username are required for this service (ArgumentError)
from /usr/lib/ruby/gems/1.8/gems/chef-0.9.10/lib/chef/knife/rackspace_server_list.rb:38:in `run'
...

If I set knife[:rackspace_username] in .chef/knife.rb as the error message suggests, and run again, I get the same error message.

It's supposed to be rackspace_api_username, which works, but Fog and Knife are using different names for the variables, and the error message from Fog gives me the wrong name of the needed variable.