Casting int[] to ubyte[]: element wise cast or slice cast

[Dennis]

I assumed that casting an int[] to a ubyte[] would keep all bytes 
and quadruple the length of the original array. But when the 
array is a literal, it keeps the same length but truncates every 
int element to a ubyte:

```
import std.stdio;

void main()
{
     // enum:
     enum litA = [0x10203040, 0x50607080];
     pragma(msg, typeof(litA));
     ubyte[] a = cast(ubyte[]) litA;

     // auto:
     auto litB = [0x10203040, 0x50607080];
     pragma(msg, typeof(litB));
     ubyte[] b = cast(ubyte[]) litB;

     writeln(a);
     writeln(b);
}
```

Prints:
```
int[]
int[]
[64, 128]
[64, 48, 32, 16, 128, 112, 96, 80]
```

I looked at the spec and found this:

https://dlang.org/spec/expression.html#cast_expressions
"Casting a dynamic array to another dynamic array is done only if 
the array lengths multiplied by the element sizes match. The cast 
is done as a type paint, with the array length adjusted to match 
any change in element size. If there's not a match, a runtime 
error is generated."

So is this a bug or am I missing something?