fixes issue #348: perf optimization during diffing algo to avoid calling addVNodes and removeVNodes when there is nothing to do.
fixes issue #348: perf optimization during diffing algo to avoid calling addVNodes and removeVNodes when there is nothing to do.

paldepind/snabbdom,snabbdom/snabbdom,snabbdom/snabbdom,snabbdom/snabbdom,snabbdom/snabbdom,paldepind/snabbdom