[:simple] Require a made up namespace does not work

Test case:

```
lein browser-repl* <- asterisk cleans
...
cljs.user=> (ns foo.bar.bar)
nil
foo.bar.baz=> (require 'foo.bar.baz)
No such namespace: foo.bar.baz, could not locate foo/bar/baz.cljs, foo/bar/baz.cljc, or Closure namespace "foo.bar.baz"
```

Probably a regression.
