Cut down on environment copies by using a proxy Environment class to hold override dictionaries from Builders and targets.
Cut down on environment copies by using a proxy Environment class to hold override dictionaries from Builders and targets.

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