I have found the need to add
near the top of vxl/vil/vil_warp.cxx. Without this, and with certain compiler options (no
optimization), no vtable was output for the vil_warp_mapping object, defined in vil_warp.h.
Can someone with a bit more VXL experience make this change if they feel it is right? I'm hesitant
to make a change myself in the core VXL files.