corebase runloop integration

[Luboš Doležel]

Hi,

I've started pushing more code into corebase (CFStream implementation, 
not thread safe for now) and did some very initial work in corenetwork. 
Unfortunately, I can't complete my work until CFRunLoop is functional.

I've worked hard on toll-free bridging, with most common types already 
bridged by now. One of the biggest remaining hurdles is the lack of 
integration between NSRunLoop and CFRunLoop. These two are not toll-free 
bridged, NSRunLoop is rather supposed to be implemented on top of 
CFRunLoop, as CFRunLoop is much more powerful.

Now, since NSRunLoop is a very important component of the whole 
ecosystem and I think we want to avoid the dependency of gnustep-base on 
corebase (it would form a loop, and corebase is neither complete nor 
extensively tested), I think the right way forward would be to add a 
second implementation of NSRunLoop that would only be used if corebase 
is loaded by the application. I'd call it NSCFRunLoop, for example.

My idea would be to use a weak reference to CFRunLoopGetCurrent() and 
somewhere in NSRunLoop's initialize make a permanent decision, which 
implementation to use based on CFRunLoopGetCurrent being NULL or not.

It will take me some time to get to this point, but first I'd like to 
hear your thoughts.

Regards,
--
Luboš Doležel