Improve warning messages coming from the CHARMM parsers.

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

@@ -341,7 +341,8 @@ class CharmmParameterSet(object):
                     replaced = False
                     for i, dtype in enumerate(self.dihedral_types[key]):
                         if dtype.per == dihedral.per:
-                            # Replace. Should we warn here?
+                            # Replace. Warn if they are different
+                            if dtype != dihedral:
                                 warnings.warn('Replacing dihedral %r with %r' % 
                                               (dtype, dihedral))
                             self.dihedral_types[key]

wrappers/python/simtk/openmm/app/internal/charmm/topologyobjects.py

@@ -926,6 +926,10 @@ class DihedralType(object):
         self.per = int(per)
         self.phase = float(phase)
 
+    def __repr__(self):
+        return "<DihedralType: k=%s; phase=%s; per=%s>" % (self.phi_k,
+                self.phase, self.per)
+
     def __eq__(self, other):
         return (self.phi_k == other.phi_k and self.per == other.per and
                 self.phase == other.phase)