Added project-dependency-based VS .sln generator

Added the ability to emit a code browsing solution for
a particular project and its dependencies, using e.g.
    self.projectMan.add_cb_project_root(self)
The above produces output of the form
'${projName}_vs2012.sln'.

The existing generator has been preserved.  It produces
outputs of the form 'all_vs2012.sln'.