Made sure FilterEngine instances are always initialized

This turned out quite a bit more complicated than expected. A JS callback needs to call JsEngine that in turn notifies FilterEngine. LazyFileSystem had to change to actually return a result that looks ok - otherwise filter engine initialization can never complete. And googletest macros had to be set because otherwise classes defined by it will conflict with <tr1/functional> that we include.

[Felix Dahlke, 2013-05-22 15:13:44]

I think it'd be nicer if JsEngine was not involved here, only FilterEngine is
being initialised.

But I can see that this is a bit more tricky to do, so LGTM.

[Wladimir Palant, 2013-05-22 20:35:10]

Thinking a bit about it, we probably need a generic messaging mechanism that
allows JS code to notify callbacks in C++ anyway (e.g. for subscription status
changes). So I can probably implement that in JsEngine and make filter engine
initialization use it.

[Wladimir Palant, 2013-05-23 06:40:36]

New patch set uploaded with a generic _triggerEvent() function instead of
_initDone(). Only one callback per event and no event parameters at the moment
to keep things simple - we can still add this later if we need it.

[Felix Dahlke, 2013-05-23 08:36:06]

LGTM, I prefer it this way :)