Fixes possible DoS if a file description has its status changed. #452
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If a file description has its status flags changed through fcntl, either by another thread/process, a possible DoS might arise, as either recv or send will block. This is an attempt to fix that, by using the MSG_DONTWAIT flag on calls to recv and send.
These are the spots where, to the best of my understanding, the operation should be non blocking.