When the client sends us a bogus URL it is not a internal server error.

* subversion/mod_dav_svn/repos.c:
  (davn_svn_split_uri): Use 404 error codes for errors caused by invalid URIs.
    


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1542063 13f79535-47bb-0310-9956-ffa450edef68