support directory factory/provider for custom direcory

[GoogleCodeExporter]

What version of the product are you using? On what operating system?
3.1.0

Please provide any additional information below.

Currently a constructor accepting a File is needed for a custom directory.
It would be nice to use a more generic approach, like a provider or factory 
interface.
Inspiration can be found in the hibernate search directory provider.
http://docs.jboss.org/hibernate/search/3.3/api/org/hibernate/search/store/Direct
oryProvider.html

For example something like

public interface DirectoryProvider {
    public void start();
    public void stop();
    public Directory getDirectory();
}

Original issue reported on code.google.com by michael....@gmail.com on 2 May 2011 at 1:56

[GoogleCodeExporter]

This doesn't sound like a common need ... if you think you could come up with a 
patch that is useful to other users please attach it here, and we'll see. 
Thanks!

Original comment by sig...@gmail.com on 28 Dec 2011 at 3:10