work correctly with GCC >= 4.0, while doing nothing for GCC < 4.0
- Add class sgpem::schedulable to test for DSO visibility export.
Methods may need to be reordered to conform to coding style guidelines
git-svn-id: svn://svn.gna.org/svn/sgpemv2/trunk@244 3ecf2c5c-341e-0410-92b4-d18e462d057c