Refactor the scons_subst*() tests to make it easier to add tests and to more completely characterize the current behavior.
Refactor the scons_subst*() tests to make it easier to add tests and to more completely characterize the current behavior.

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