In amok_bw_test, it is now possible to ask that the measurement lasts at least N...

In amok_bw_test, it is now possible to ask that the measurement lasts at least N seconds (N being a double). If it is not the case with the provided msg_size, it will get adjusted and a new test is made (using the same measurement sockets so you won't pay the handshaking twice). This mecanism is still to be offered in amok_bw_request(), but I'm on it.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@2334 48e7efb5-ca39-0410-a469-dd3cf9ba447f