Reorder pre and post arcs using the order of variables.
Merge branch 'master' into reorder_pre_post
Merge branch 'master' into reorder_pre_post
Merge branch 'master' into reorder_pre_post
Merge branch 'master' into reorder_pre_post

Conflicts:
	src/mc/classic/worker.cc
Merge branch 'master' into reorder_pre_post

Conflicts:
	src/mc/classic/worker.cc
Merge branch 'master' into reorder_pre_post