hhh4(): 
- support for lag != 1 (+ report non-default lag in summary)
- started support for parallelization of oneStepAhead()
- less hhh4-method dispatch by calling .hhh4-methods directly


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@798 edb9625f-4e0d-4859-8d74-9fd3b1da38cb