mac: CFRunLoop/CFSocket incompatible with select() on the same socket

This problem is similar to the Blackberry problem.

Whenever we create a CFSocket in qcfsocketnotifier.cpp (due to the Cocoa-based event loop for the GUI thread), it registers the socket for notification with an outside source (kevent, threads, whatever). That is incompatible with the select()-based loop we have in qprocess_unix.cpp.

The attached "bad" output of dtruss shows that the following happens (note, dtruss output is not ordered, you should sort by thread CPU time):

1. parent process stops in select(), waiting for input from child (this is QProcess::waitForReadyRead)
2. child process writes "hello world"
3. parent process reads, first by doing an ioctl with FIONREAD
4. parent process goes into the CFRunLoop-based processEvents()
5. the socket notifier for the stdout channel is activated
6. parent process tries to read, but this time ioctl reported 0 bytes available
7. parent process closes stdout channel
8. child process writes to stdout and gets EPIPE and dies from SIGPIPE