Fixing support for library dot notation when using URL compact syntax

In _parseString(), including . (dot) character in the regex pattern, for matching "compact syntax" paths with dot notation specifying the library.

Prior to this update, library dot notation did not work when using compact URL syntax. For example,

$url = Router::match(array('myplugin.Posts::view', 'id' => '1138'));

failed because the . character within the controller component ('myplugin.Posts') is 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.