bug fix in mob(), bumped devel version to 0.8-3

the bug occured only if some regressor variables were also used as
partitioning variables and the corresponding columns were not sorted
in the model frame



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/partykit@616 255f4249-2263-4417-b1ea-8498779e27a7