Try to improve getline portability...

Try to improve getline portability...

In the configure, you test for the presence of getline using
    #define _GNU_SOURCE
    #include <stdio.h>
So it is detected as functionnal on my machine (hardy) but if you do
not put these lines in simgrid_config.h it will break. The only thing
is that other headers may include stdio.h earlier in which case the
later _GNU_SOURCE will be useless... :(

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@6893 48e7efb5-ca39-0410-a469-dd3cf9ba447f