Add option for skipping copying / restoring old builds of workspaces

A project using a cloned workspace as input allways restores / copies the workspace, no matter, if it has changed or not.

It would be nice to be able to skip that step, in case the input-workspace has not changed / was not rebuild.

In our case I have a prebuild slow-changing workspace as start environment for testing some rapidly changing modules (using some scripts to update them). Here it would be usefull, if the workspace would be restored only, if it has changed.