FuXi cannot handle existentials in the head

```
FuXi cannot handle existential in the head despite the fact that there are 
several approaches for handling such situations.  This issue can be reproduced 
via this test case: 
http://code.google.com/p/fuxi/source/browse/test/testExistentialInHead.py

```

Original issue reported on code.google.com by `chime...@gmail.com` on 12 Nov 2011 at 2:17
- Blocking: #59
