Fix running tests in subdir as argument to runtest.py, e.g.
Fix running tests in subdir as argument to runtest.py, e.g.

    python runtest.py test/CC

andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons,andrewyoung1991/scons