Here's a patch skipping testFDPassSeparate and
testFDPassSeparateMinSpace on OS X < 10.5, due to known kernel bugs
(see http://developer.apple.com/library/mac/#qa/qa1541/_index.html).
For InterruptedSendTimeoutTest and testInterruptedSendmsgTimeout, it
also looks like a kernel bug.
There could be another explanation, though: if, for some reason, other
threads are running at that time, the signal might be delivered to
another thread, and our main thread remains stuck on sendto/sendmsg
once the socket buffer is full. I'm however not sure why this would
only affect OS X (since FreeBSD behaves in the same way when it comes
to signals, contrarily to Linux). Also, I'm not sure why this would
not affect recv/recvmsg.