Always create aliases for non-namespaced classes

This fixes the following problem:

**Expected**
```sh
$ xp -w 'try { raise("webservices.rest.RestException", "test"); } catch (\webservices\rest\RestException $expected) { return "OK"; } return "FAIL";'
OK
```

**Actual** 
```sh
$ xp -w 'try { raise("webservices.rest.RestException", "test"); } catch (\webservices\rest\RestException $expected) { return "OK"; } return "FAIL";'
Uncaught exception: Exception lang.reflect.TargetInvocationException (xp▒runtime▒Dump::main)
  at lang.reflect.Method::invoke(NULL, array[1]) [line 95 of class.php]
Caused by Exception webservices.rest.RestException (test)
```