[dmd-internals] Add a ghostNode Hierachy ?

[Stefan Koch via dmd-internals]

Hi,

In DMD's AST we have something I'd like to call gohstNodes.
That is nodes which get lowered into others.
For example a the foreach-loop, the do while, while and do until 
loop.
Are all lowered into a for loop.

making the others into a ghost node which is never supposed to 
appear.
yet every visitor checks for them explicitly.

If all of those were a subclass of ghostnode which in turn would 
be a subclass of RootObject.
Then one visit overload would suffice to catch them all.