Hi,
Here is patch for convertion to absolute path for removed files. If file has been removed in repository, "svn info" returns error. So if somebody tries to generate diff for revision where file has been removed, it generates incorrect diff (without absolute path, i.e. with branch information). As result, such diff can't be submitted to ReviewBoard instance. 
The fix is simple and safe. To fetch file path prefix it calls "svn info ." instead of "svn info file", i.e. get information for root folder which exists in any way. Then it concatenates prefix and relative path.
Please review it!
Thank you in advance!