NAME   zone_picker - display, pick and transform zone transitions on wells 
  
AUTHOR Ian J. Curington, Advanced Visual Systems Inc.

DESCRIPTION
   This routine takes two 1D  inputs, one the
   zonation table, and second, the deviation file
   for one 3D well track. 
   It creates a geometric representation of the zonation picks
   along the well bore, as golden rings,
   and allows picking and dragging of the positions for
   editing.
  
   It looks at the labels on the well dev field to figure
   out which well it is, then indexes the zonations by this,
   so there is no menu selection needed here.
  
   the zone icons can be picked and dragged along the well,
   the new positions recorded in the memory file structure.
  
   NOTE: Advanced Module Technique:
   This routine contains an advanced module writer trick,
   of modifying the input port data inplace, without
   explicitly or implicitly copying the data out of shared memory.
   This REQUIRES that a special flag be turned on in
   your .avsrc file:
   ReadOnlySharedMemory 0
  
   If you get it wrong, you will either get a shared memory
   access violation, or when the module is killed a message like:
     zone_picker: AVSfield_free: bad 'refcnt' 0, field=0x00072e10