Detect socket closed by peer in the transport layer, so that such things don't polute...

Detect socket closed by peer in the transport layer, so that such things don't polute the messaging layer. This is done by recv() on the socket, which is not allowed on 'file sockets'. So, add a property to the sockets indicating whether it is ok to recv() on the socket or not, and then use it right after the select to detect dead horses

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@2433 48e7efb5-ca39-0410-a469-dd3cf9ba447f