please add sanity checking for key:location values

[RicoZ]

Documented values are underground, underwater, overground, overhead, roof

​http://wiki.openstreetmap.org/wiki/Key:location

Of those 5 I am not sure I would endorse location=roof but it widely used and at least not completely wrong.

The list of used values in taginfo is currently 8181 items, many of them road names which were perhaps supposed to be addr or whatever else.

​http://taginfo.openstreetmap.org/keys/?key=location#values