Add a method to check whether ABP is fully initialised

This allows clients to wait until ABP is fully initialised, which is necessary for adding subscriptions.

I'm aware that this is not what you had in mind Wladimir, it would be cleaner to just pass the user language in through AppInfo and select an appropriate default subscription in libadblockplus. However, it would also take a bit longer to implement. Would you mind going with this for now?

[Wladimir Palant, 2013-05-15 15:51:59]

Mostly LGTM, we need this API regardless of the subscription adding approach.
However, we also need a way to wait for the engine initialize - ideally
something that doesn't involve Sleep() and polling.

[Felix Dahlke, 2013-05-16 02:50:18]

On 2013/05/15 15:51:59, Wladimir Palant wrote:
> Mostly LGTM, we need this API regardless of the subscription adding approach.
> However, we also need a way to wait for the engine initialize - ideally
> something that doesn't involve Sleep() and polling.

We could have a callback that's invoked once ABP is initialised, but I'm
thinking AdblockPlusEngine would still need to wait for that before it accepts
client connections.

[Wladimir Palant, 2013-05-16 11:54:28]

On 2013/05/16 02:50:18, Felix H. Dahlke wrote:
> We could have a callback that's invoked once ABP is initialised, but I'm
> thinking AdblockPlusEngine would still need to wait for that before it accepts
> client connections.

Exactly my point - it can wait for the callback rather than polling the filter
engine.

[Wladimir Palant, 2013-05-16 12:15:30]

Alternatively we can simply make FilterEngine constructor wait until everything
is initialized and only return then.

[Felix Dahlke, 2013-05-17 08:43:51]

On 2013/05/16 12:15:30, Wladimir Palant wrote:
> Alternatively we can simply make FilterEngine constructor wait until
everything
> is initialized and only return then.

Closing this review, since you addressed that in a new one:
http://codereview.adblockplus.org/10420020/