prunes non-initial rules (i.e. rules with non-terminals) from the rule table
based on their frequency counts. In Zollmann, Venugopal, Och, and Ponte (2008),
pruning hierarchical rules that occur only once was found to significantly
decrease rule table size without harming translation quality.
Also, add TUNING:filter-settings and EVALUATION[:<set>]:filter-settings
variables so that this can be enabled in the EMS.
git-svn-id: https://mosesdecoder.svn.sourceforge.net/svnroot/mosesdecoder/trunk@4033 1f5c12ca-751b-0410-a591-d2e778427230