hashes of hashes not supported

[Maxim Fomin]

On Friday, 9 November 2012 at 13:15:15 UTC, Dan wrote:
> ...

Actually error message is:

Error: function hello.S.__postblit () is not callable using 
argument types ()
Error: *&this is not mutable
Error: this is not mutable
Error: this is not mutable
hello.d(6): Error: template instance 
object.AssociativeArray!(string,const(S)) error instantiating

Making postblit accept const this makes dmd happy.

Seems to be caused by S[S[string]] which requires "this" to be 
const.