Reduce code bloat

This hack isn't needed in 0.4 anymore, so instead of trying to fix
this for 0.3, I think we should just scrap it and let interpolation
objects show their elements as #undef until 0.4 ships. Not sure we'll
be ready to release Interpolations until then anyway...
Merge pull request #15 from tlycken/multidim-display

Multidimensional display isn't working properly