can now only happen if the thread is killed.
_user_receive_data() will now longer pass B_CAN_INTERRUPT to receive_data(),
but B_KILL_CAN_INTERRUPT - this should fix the problem Stefano experienced
with this function, even if I couldn't reproduce it.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@13075 a95241bf-73f2-0310-859d-f6bbb57e9c96