Safer D first draft

[Richard (Rikki) Andrew Cattermole]

Thanks for the reminder, ``a.ptr`` is a perfectly safe operation, it 
exists solely because we do not have type state analysis to prevent 
dereferencing null. It can be a valid argument to non-D code both as 
null and non-null. That check should be removed.

I see there is one other example given, for escape analysis. This is 
where I actually see the value in such a proposal and have thought about 
as part of my own proposals.

Specifically for type state analysis, it is never correct to dereference 
null, therefore it should never be allowed in ``@system` code.