Sometimes, the time to wait is soo small that the increment does not change the globa...

Sometimes, the time to wait is soo small that the increment does not change the global clock (for example, 100000 + 10E-15=100000). Add an epsilon to the wait to avoid the issue. I'm still not completely sure that the fix is 100% effective (because 10E300 + 1 = 10E300), but I don't have any better idea

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@5436 48e7efb5-ca39-0410-a469-dd3cf9ba447f