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tickbox variable: $readsurf2flag -- read 2nd surface
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keyboard equiv: none

If the "2" checkbutton is ticked, clicking the
"R" button just to the left of it reads in (or
re-reads) a second surface (read_binary_surface2)
and colors it green.

If the "2" button is unticked (default at
startup), a first surface is read in (or re-read)
and colored yellow.

HOWTO display lh.orig (yellow) and lh.pial (green)

  0) untick "2" (default)
  1) select lh.orig from "surf:" dropdown
  2) click "R" on "surf:" line
  3) tick "2"
  4) select lh.pial from "surf:" dropdown
  5) click "R" on "surf:" line
