straighten tainted conditions

some of those made a multipolygon tainted even though they were
simply incomplete data.
add tests for multipolygons

* non-trivial ring building
* unclosed rings

(and added some inline explainations and remove some dead code)
ordering
add one-node-ways test
add tests for polygon detection
add tests for callback options (polygon detection and uninteresting tags)
fix bug: wrong (inverse) logic in uninterestingTags callback evaluation