Memory consumption with large projects

[David Nolden]

I don't have time to exactly look at your massif output, but neither the 
token-stream, nor the AST should live for a long time.

Both of these are just temporary objects, that should be deleted once the 
parsing is completed, unless the TopDUContext::AST feature is set, in which 
case the stuff is attached to the du-context. However that feature is not used 
during normal parsing, so that stuff should not really show up in the massif 
output.

So we have to find out why the AST and token-stream are not deleted. I 
remember having checked that at some point, but I think I came to the 
conclusion that they were deleted properly. The whole stuff is stored in the 
ParseSession object. But as I said, no time for this right now, as I have an 
exam in monday.

Greetings, David