Initializing a field with itself has been deprecated

This is to prevent a common mistake when a field and a parameter ought to have the same name,
but one is misspelled where it's declared:

---
struct S
{
    int field;

    this(int feild) // supposed to be: this(int field)
    {
        this.field = field; // equal to this.field = this.field
    }
}
---
