Change sg_unit_extractor so that it takes all units to generate on its command line...

Change sg_unit_extractor so that it takes all units to generate on its command line. That way, make don't have to call it several times, and this is good because parallel invocations of the script were subject to breakage since they all change the same src/sg_main_tests.c file (in short, fix parallel build of the tool)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@6009 48e7efb5-ca39-0410-a469-dd3cf9ba447f