* Modification of the mapping is possible now
(#map used to ignore mappings if there was one
already)
* Added DropCell mapping (also for RBA)
* Added unit tests for cell mapping, layer mapping
db::merge_layouts, db::copy_shapes and db::move_shapes
- Include a copy of the unit test framework so we're no longer
depending on incompatible versions for Ruby 1 and 2.
- Avoid duplication of path entries in unit tests