Linked the CFNetwork framework as an optional framework into MCGraylog. The default linking was causing link errors on 10.7.

Calling graylog_init_socket on 10.7 will crash, but at least it can link and run now.
Fix NSDate usage to be compatible with OS X 10.7

At least one implementation of NSDate.date returns an id on Lion and
Xcode, or the compiler, are using the return type from that
implementation and so we have a type issue when using the dot syntax.