Fix a vicious bug: TCP socket use a buffer and read operation get as much data as...

Fix a vicious bug: TCP socket use a buffer and read operation get as much data as possible. It is possible that several messages are received in one shoot, and select won't catch them afterward again. Instead, the select will block and the surnumerous messages are lost.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@2671 48e7efb5-ca39-0410-a469-dd3cf9ba447f