Optimizing the closed-way case in multipolygons #156
Description
Current code assembles multipolygons in the same way regardless of whether they are created from a closed way or from a multipolygon relation. This might be wasteful. Chances are the closed-way case can be made faster because it is simpler. Profiling shows that closed-way multipolygons take a considerable amount of time compared to relation-based multipolygons.