renamed "splits" argument to "dfsplit" because this is clearer
and now integer arguments (e.g., dfsplit = 3) are also supported

added rather detailed description of pruning strategy in mob.Rnw



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/partykit@446 255f4249-2263-4417-b1ea-8498779e27a7