-------------------------------------------
funct (left-click): write curr area to file
  set area <outfile>
  write_binary_areas
-------------------------------------------

The "W" button on the "area:" entry line writes
out vertex-wise local surface area for the
current surface to the file: $area (name
currently in entry to left).  The data written
out comes from the .area field (N.B.: *not* from
the .origarea field).

There is a warning if you try to overwrite
$hemi.area, the "original area" file, which is
generated at surface-making time, and which is
always read by tksurfer at startup, regardless of
which surface is displayed (in order to be able
to report original-surface areas of labels).

This is similar to the handling of the original
3D surface vertex coordinates.

N.B.: the write_binary_area function NO LONGER
copies the contents of the .area field to the
.origarea field (old confusing behavior where
current surface area is re-defined as "orig").
To do this, instead simply read in the file just
written with the "R" button.
