newCTFE: perliminary delegate support is in!

[Stefan Koch]

Good day ladies and gentleman,

it is my distinct please to announce that a new feature just 
landed in newCTFE.

!!! DELEGATES !!!

this means the following code will now work:
int square_of_x_plus_x(int x) pure
{
     int passThrough(int y) pure
     {
         assert(x == y);
         int y2 = x;
         assert(y2 == y);

         int fnC() pure
         {
             auto z = (x * y);
             assert(y2 == x);
             assert(x == y);
             return z;
         }
         return fnC();
     }
     return x + passThrough(x);
}

pragma(msg, square_of_x_plus_x(7));
static assert(square_of_x_plus_x(5) == (5*5)+5);

the reason why this was quite tricky to implement is that
in the newCTFE architecture there is no concept of a function 
touching
the stack-frame of another function _at all_.
(Infact there is  no conventional stack, rather the virtual 
registers themselves stack)
Sharing of the stack frames gets emulated via a hidden parameter 
and a linked-list structure.

Cheers,
Stefan