Fix a formula issue when all levels have the same ID; each levID corresponds to an integer number in the decreasing order 

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/r2mlwin@222 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Use sparseby in the reshape package (if installed) to reduce memory usage when calculating model hierarchy information.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/r2mlwin@223 edb9625f-4e0d-4859-8d74-9fd3b1da38cb