Consider latin1 non-breaking spaces (aka &160;) as spaces, and don't include them when autolinking

The non-breaking space (`0xA0`, `&160;`, ` `) doesn't get counted as a space currently. 

Before patch: 

``` ruby
> helper.auto_link("http://github.com is great")
=> "<a href=\"http://github.com is\">http://github.com is</a> great" 
```

After patch:

``` ruby
> helper.auto_link("http://github.com is great")
=> "<a href=\"http://github.com\">http://github.com</a> is great" 
```