Fix off-by-one corner case discovered during testing of /user/profile.

Added getSingleIndexedParamValue() that retrieves an index into a list of values from the named query parameter, and then indexes into the supplied list of values to return the corresponding value from the list. Used to convert numeric index query parameters passed by POST to the GET redirect target, so that the GET code can display messages, etc. (without passing the message itself as a query argument and having to escape it or have silly people pass in their own...).

Added replaceSuffix(), isReferrerSelf(), and redirectToChangedSuffix() to implement the TODO in the User profile views where the link name portion of the URL needs to change when the link_name Property is updated by the form.