I've got this working. In addition to what you did, I also enabled ssh keys between review board and git. To do this I did the following:
- in the review board admin "system setting / ssh" admin screen, Generate a key, then set that key in .ssh/authorized_keys on the git server.
- I also manually created a key (as root) on the git server (with ssh-keygen) and add that key to .ssh/authorized_keys on the git server.
I also set the raw file url mask to:
http://[ipaddr]/cgi-bin/gitweb/gitweb.cgi?p=reponame.git;a=blob_plain;f=<filename>;h=<revision>
If that doesn't work, you'll probably have better luck asking on the review board support forum (https://groups.google.com/forum/#!forum/reviewboard) some of the maintainers seems to reply to problems there regularly.