Correcting vff tests

  * Some issues with newer/older versions of quantities
  * Disabled some tests if scipy < 0.11.0
Changed how to include tests in compilation

  * Tests are now separated into normal tests, and tests that require an
    external program to run (such as vasp)
  * At this juncture, all normal tests should run and pass, always.
  * Other tests may depend on the existence, version, whatnot, of the external
    program.