post-review assumes it is being called from within a working copy.  My company performs post-commit reviews (despite the drawbacks), and we wanted our subversion post-commit hook to automatically create review requests.  To be usable without a working copy, post-review needs to operate relative to a repository URL.  

I added a REPOSITORY_URL global config variable (note that it can't be provided via a command line option since it's used in get_repository_info before the options are parsed).  If post-review is called outside a working copy, this URL is used for creating diffs if a revision range is provided.  If the diff is created using the URL, the Subversion diff file mangling is altered slightly.

I also fixed checking for a homepath to not fail if there is no HOME variable available (i.e. when post-commit is called by svnserve).  This seems safe, since homepath is only used to find an optional cookie.

Posted review requests to local review board instance using configured SVN repository URL.  Tested with subversion 1.4.4 and 1.5.2