[Opencxx-users] add PtreeVisualizer.h to branch rel_2_8

[<se...@in...>]

required by opencxx/opencxx/parser-test.cc
$ ./parser-test
digraph Ptree {
  node[shape=box,width=.1,height=.1];
  _0x9374bf8[label="PtreeDeclaration",style=bold];
  _0x9374bf8 -> _null0[taillabel="CAR"];
  _null0[shape=point,label=""];
  _0x9374bf8 ->  _0x9374c08[taillabel="CDR"];
  _0x9374c08[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374c08 ->  _0x93742e8[taillabel="CAR"];
  _0x93742e8[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x93742e8 ->  _0x93742d8[taillabel="CAR"];
  _0x93742d8[label="LeafINT\nint",style=filled,fillcolor=lightgray];
  _0x93742e8 -> _null1[taillabel="CDR"];
  _null1[shape=point,label=""];
  _0x9374c08 ->  _0x9374c18[taillabel="CDR"];
  _0x9374c18[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374c18 ->  _0x9374b58[taillabel="CAR"];
  _0x9374b58[label="PtreeDeclarator",style=bold];
  _0x9374b58 ->  _0x9374ae8[taillabel="CAR"];
  _0x9374ae8[label="Leaf\nmain",style=filled,fillcolor=lightgray];
  _0x9374b58 ->  _0x9374b28[taillabel="CDR"];
  _0x9374b28[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374b28 ->  _0x9374b18[taillabel="CAR"];
  _0x9374b18[label="Leaf\n(",style=filled,fillcolor=lightgray];
  _0x9374b28 ->  _0x9374b38[taillabel="CDR"];
  _0x9374b38[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374b38 -> _null2[taillabel="CAR"];
  _null2[shape=point,label=""];
  _0x9374b38 ->  _0x9374b48[taillabel="CDR"];
  _0x9374b48[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374b48 ->  _0x9374b08[taillabel="CAR"];
  _0x9374b08[label="Leaf\n)",style=filled,fillcolor=lightgray];
  _0x9374b48 -> _null3[taillabel="CDR"];
  _null3[shape=point,label=""];
  _0x9374c18 ->  _0x9374c28[taillabel="CDR"];
  _0x9374c28[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374c28 ->  _0x9374ba8[taillabel="CAR"];
  _0x9374ba8[label="PtreeBlock",style=bold];
  _0x9374ba8 ->  _0x9374bb8[taillabel="CAR"];
  _0x9374bb8[label="Leaf\n{",style=filled,fillcolor=lightgray];
  _0x9374ba8 ->  _0x9374bd8[taillabel="CDR"];
  _0x9374bd8[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374bd8 -> _null4[taillabel="CAR"];
  _null4[shape=point,label=""];
  _0x9374bd8 ->  _0x9374be8[taillabel="CDR"];
  _0x9374be8[label="NonLeaf",color=lightgray,fontcolor=lightgray];
  _0x9374be8 ->  _0x9374bc8[taillabel="CAR"];
  _0x9374bc8[label="Leaf\n}",style=filled,fillcolor=lightgray];
  _0x9374be8 -> _null5[taillabel="CDR"];
  _null5[shape=point,label=""];
  _0x9374c28 -> _null6[taillabel="CDR"];
  _null6[shape=point,label=""];
}
$