Blocks shouldn't be able to call themselves, or if they can, there should be some restrictions placed on it

This causes the compiler to hang:
```
block foo(a b) {
return foo(1 1)
}

led(foo(0 0))
```

So does this:
```
block foo(a b) {
return bar(1 1)
}

block bar(a b) {
return foo(1 1)
}

led(foo(0 0))
```