KDTreeFlann::SetRawData had some confusion around data, data_, and
data_interface_. As a result, the data from the parameter was copied to
the member std::vector, but the interface (which takes an Eigen::Map)
used the data passed as an argument to the method.
As a result, the searches risked to be run on a dangling pointer,
instead of the intended internal storage.

However, rather than adjusting the pointer for Eigen::Map, I preferred
simplifying the code, and copy the argument to an Eigen::MatrixXd.

…data