Fixing support for library dot notation when using URL compact syntax

In Router::_parseString(), adding . (dot) to regex character class, for matching library-based routes specified in "compact syntax," e.g., 'myplugin.Posts::index'

Prior to this update, library dot notation did not work when using compact URL syntax. For example:

```php
$url = Router::match(array('myplugin.Posts::view', 'id' => '1138'));
```

This failed because the . character within the controller component ('myplugin.Posts') was unrecognized by _parseString(). By including the . character in the regex pattern, the above compact URL path will not fail, and the controller portion, "myplugin.Posts" will subsequently be parsed by _parseController(), which recognizes the library dot notation.