OS X Overlay Icons: Fix Finder plugin crash

By enabling ARC for GCDAsyncSocket (as we should have done before
https://github.com/robbiehanson/CocoaAsyncSocket/wiki/ARC) there
is no chance anymore for a situation where the to-be-written NSData*
is deleted before the socket has had a chance to write it.
Interestingly, this only happened after switching to local sockets,
probably because of how immediatly the NSData* would be sent.

This commit also keeps the debug symbols for the Finder plugin.