Eponymous template with static if

[Michael Galuza]

It's well known that template functions in D are just kind of 
eponymous template:
```d
T square(T)(T t) {
     return t * t;
}
```
is lowered to
```d
template square(T) {
     T square(T t) {
         return t * t;
     }
}
```

But if we write this:
```d
template square(T) {
     static if (true) {
         T square(T t) {
             return t * t;
         }
     }
}
}
```
trivial expression `square(3)` won't compiled with message
`Error: none of the overloads of template main.square are 
callable using argument types !()(int)`.

Why? What I missed?