I think I now better understand the surf internals: each resource can be *either...

I think I now better understand the surf internals: each resource can be *either* a cpu or a link, so we can merge all the get_??_properties into only one method. No object will need both of them. This could be further improved by moving this to a function in surf directly instead of leaving this in models, but it would be the first attribute being handled that way, so I prefer keeping the pseudo object philosophy in place in surf

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@4895 48e7efb5-ca39-0410-a469-dd3cf9ba447f