Minor fixes

wrappers/python/simtk/openmm/app/amberprmtopfile.py

@@ -94,7 +94,7 @@ class AmberPrmtopFile(object):
                 try:
                     element = elem.get_by_symbol(atomName[0])
                 except KeyError:
-                    pass
+                    element = None
             top.addAtom(atomName, element, r)
         
         # Add bonds to the topology

wrappers/python/simtk/openmm/app/forcefield.py

@@ -249,7 +249,7 @@ class ForceField(object):
          - nonbondedMethod (object=NoCutoff) The method to use for nonbonded interactions.  Allowed values are
            NoCutoff, CutoffNonPeriodic, CutoffPeriodic, Ewald, or PME.
          - nonbondedCutoff (distance=1*nanometer) The cutoff distance to use for nonbonded interactions
-         - constraints (object=None) Specifies which bonds angles should be implemented with constraints.
+         - constraints (object=None) Specifies which bonds and angles should be implemented with constraints.
            Allowed values are None, HBonds, AllBonds, or HAngles.
          - rigidWater (boolean=True) If true, water molecules will be fully rigid regardless of the value passed for the constraints argument
          - removeCMMotion (boolean=True) If true, a CMMotionRemover will be added to the System