Add a couple unittests for CHARMM files.  Good thing, too, because they helped
pick up some bugs that were not caught in my initial test following the port
from ParmEd.

All 4 tests pass right now, although no periodic systems are being tested.
Currently CHARMM, XPLOR, and VMD tests are all being run (for the same ala-3
system).

Disable implicit solvent tests, since there is no robust radii assignment
routine yet (the radii are stored in the Amber topology file).  I will port my
assignment routine from ParmEd here shortly and then re-enable the GB tests.