Completion of . (dot) terminates shell process

Hi,

I run into an error when I try to complete (TAB) after a . (dot).

I use the elixir `HEAD` version https://github.com/elixir-lang/elixir/commit/7120a5e05053c83547c04187ceceb262a06fd023

```shell
❯ iex
Erlang R16B01 (erts-5.10.2) [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Interactive Elixir (0.10.4-dev) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> .*** ERROR: Shell process terminated! (^G to start new job) ***

=ERROR REPORT==== 30-Oct-2013::10:14:24 ===
Error in process <0.25.0> with exit value: {function_clause,[{string,tokens1,[nil,"(",[]],[{file,"string.erl"},{line,227}]},{'Elixir.IEx.Autocomplete',last_token,2,[{file,"/private/tmp/-1sUr/lib/iex/lib/iex/autocomplete.ex"},{line,112}]},{'Elixir.IEx.Autocomplete',expand...
```

cheers