ParseError is provided in lieu of TypeError for Proc config

In the following example:
```
proc driver_proc {
output_c: chan out u32;

config(output_c: chan out u32) {
(output_c)
}

next(tok: token) {
let tok = send(tok, output_c, u32:0);
(tok)
}
}
```

With the code above, the error is as follows:
```
0034: config(output_c: chan out u32) {
0035: (output_c)
~~~~~~~~~~~^------^ ParseError: The final expression in a Proc config must be a tuple with one element for each Proc data member.
0036: }
0037:
```

A TypeError would be more descriptive.