Avoid attribute soup by doing attribute-infering for function(s) of template type

[An Pham]

Sample below, F.get, get error for class expected but OK for 
value type (no indirect type). D needs to do attribute inference 
(const nothrow pure @safe) for function(s) within template type

module X;

@safe:

     struct F(T)
     {
         T[] data;

         T get(size_t i) const nothrow @safe
         {
             return data[i];
         }
     }

     struct T1
     {
         int x;
     }

     class T2
     {
         int x;
     }

     void main()
     {
         import std.stdio;

         F!T1 t1;
         writeln(t1.get(0));

         F!T2 t2;
         writeln(t2.get(0));
         /*
     onlineapp.d(11): Error: cannot implicitly convert expression 
`this.data[i]` of type `const(T2)` to `X.T2`
     onlineapp.d(32): Error: template instance `X.F!(T2)` error 
instantiating
     	*/
     }