fix creation of tmp test cachedir
fix assert message
fix diff updates of nodes with dropped tags
add use_single_id_space mapping option

Mangle way and relation IDs so that they don't colide with
node IDs for imports into a single table.
Way IDs are negated, relation IDs are negated and shifted by -1e17.
add TODO note
ignore imposm3 binary
build ZOrder on key value instead of mapping_type
support for multiple keys to include for column (extra_fields in imposm2)