[classlib][prefs] default provider of prefs

[Regis]

Hi,

The provider of prefs is controlled by the property 
"java.util.prefs.PreferencesFactory" in Harmony, and we also have 
different default values for it on Linux and Windows, but the default 
values are set in luni module at 
modules/luni/src/main/native/luni/shared/luniglob.c,
are there any special concerns that we must do it in luni native code? 
Or is it possible set it in prefs module with java code, like this:

         if (factoryClassName == null) {
             if (isWindows) {
                 factoryClassName = 
"java.util.prefs.RegistryPreferencesFactoryImpl";
             } else {
                 factoryClassName = 
"java.util.prefs.FilePreferencesFactoryImpl";
             }
         }

I think there must be a way to get current platform at runtime in java.

--
Best Regards,
Regis.