test driver now adds the build directory to the cyclus module path. fixes #592. note that this overwrites the global module variable only for the test driver's environment.
added robustness in the environmental tests by resetting the environment variable and the dynamic loading tests by making sure to delete and close opened library modules.
adjusted env var setting to append the current var if it was set
removed extraneous string var
removed pesky cout
Merge branch 'i592-2' of github.com:gidden/cyclus into gidden-i592-2