Give the option to run Forced refresh periodically

[Petr Nejedly]

In some cases the delta scan doesn't work correctly (usually due to OS / java deficiencies).

When automatic updates are on in the console, we should enable to either run delta scanning or periodic full refresh (or both?).

As a solution we will implement a system variable switch to force using POLLER, which should deal with the native scanning not always working, and there is no need to pollute the console with the switch.

The users can manage the frequency check via serviio.libraryPollerFrequency variable.

[DenyAll]

I'd suggest both. Some users may wish to use delta scanning and then do a periodic scan once a day as a safety catch-all.

[Petr Nejedly]

added serviio.forceLibraryPoller system property for forcing the usage of POLLER library scanner

[DenyAll]

Does this switch disable delta scanning? Or do you get both? What did you decide?

If both, will polled scanning still be enabled by this switch if automatic refreshing is off in the console (ie. Delta scanning disabled, but polled scanning enabled)?

[Petr Nejedly]

This means that instead of NATIVE delta scanner it'll use POLLER (even if NATIVE is supported). So this will only work with automatic refreshing. This should help in the cases where NATIVE doesn't pick up changes, is too IO expensive, etc. It makes it similar to pre-1.5 scanning (ie polling for the current state of the shared folders and comparing with what has been seen before)