BF: removed ftmp variable

Removed unreferenced ftmp variable. This is in response to issue #449. The bug had no real effect because EuDX has already very hard constrains on the boundaries. It doesn't process seeds on the boundary voxels because of limitations with the trilinear interpolation being used. Test showing that added. Thx to the tracking team with the new tracking API we have a more flexible API to deal with the boundaries. 
Is it easy to explain why this tests the changed code?