Allow omitting '/**/*' in include

This is a huge time sink for users who are going to think

``` json
"include": ["./foo/bar"]
```

is equivalent to

``` json
"include": ["./foo/bar/**/*"]
```

At the very least, we can give a warning.

Of note, `"exclude": "./foo"` seems to be equivalent to `"exclude": "./foo/**/*`, so why is there an inconsistency here?
