[Rebuild] Relations

[Ed Loach]

> I think this is very important. Removing members from a relation
in some (most?) cases will cause the relation to become
invalid/misleading/wrong. 

Like removing individual way sections from a split road will leave
it broken, or removing tags from a node will leave it broken. Things
will need fixing after the licence change and I'm not sure extra
tags are required to trace those; just use of existing QA tools to
report issues (like gaps in route or boundary relations, etc).

Ed