oct2mat script based on parse tree

[John W. Eaton]

On  8-Jan-2008, I wrote:

| I don't think you need to modify the parse tree here when you
| encounter something like "+=".  You just need to emit the lhs, then
| the binary op corresponding to the OP= operator (you can get that with
| the octave_value::op_eq_to_binary_op method) and then emit the rhs.

Oops, I meant to say

  emit lhs
  emit "="
  emit lhs again
  emit binary operator corresponding to original OP= operator
  emit rhs

jwe