-------------------------------------------
var,funct (left-click): write current patch
  set patch <outfile>
  write_binary_patch
-------------------------------------------

The "W" button on the "patch:" entry line writes
out current cut/filled state of surface as
patchfile $patch (name in entry to left).  Must
confirm overwrite, or use write_binary_patch
(doesn't ask).  Naming convention:

  $hemi.<patchtype>.patch.<3d,flat>
  (e.g., rh.occip.patch.flat)
