Fix up for reading in chemkin dup reactions

importChemkinLibrary.py was failing for a chemkin file with duplicate
reactions that are written in opposite directions (i.e., A=B and B=A).

rmgpy/data/kinetics/library.py

@@ -136,7 +136,7 @@ def markValidDuplicates(self, reactions1, reactions2):
                     ):
                     r1.duplicate = True
                     r2.duplicate = True
-
+                    
     def checkForDuplicates(self):
         """
         Check that all duplicate reactions in the kinetics library are
@@ -178,8 +178,8 @@ def convertDuplicatesToMulti(self):
                         print "Reactions isomorphic but with different reversibilities"
                         continue
                     duplicates.append(entry)
-
-            assert len(duplicates)>1
+            if len(duplicates)<=1:
+                continue
             kineticsList = []
             longDesc = ''