Csurf "load2surf:" tickbox (right)

checkbutton -- load 3D vol into tksurfer
default: off

When this checkbutton is ticked, the 3D volume to
the left (on the VOLUME line) is loaded into
tksurfer when the lower-left SURFACE button is
clicked.

The 3D image goes into the primary buffer used
for re-positioning surfaces to generate, for example,
white and pial surfaces.

This check is immediately unticked, whether or
not the volume was successfully loaded.
