const of AliasSeq is silently ignored

[Yuxuan Shui]

In this example:

     const(AliasSeq!(int, int)) a;
     pragma(msg, typeof(a)); // (int, int)

This kind of make sense, since AliasSeq is not a "single" type. 
But silently dropping const seems bad, the compiler should 
probably report an error/warning in this case?