TestGenerateProgram/regress-node-12507 fails

[Frassle]

Error: Failed to generate YAML program: *model.IndexExpression

  on regress-node-12507.pp line 15:
  16:   localGatewayRouteTableId            = rts.ids[range.value]

Unimplemented! Needed for  rts.ids[range.value]

I had a look to see if this was easy to fix, Looks like `expr(e model.Expression) in gen_program,go needs to check for IndexExpression but wasn't clear how to correctly translate that to YAML.