Bug 720955. (Av1) xpt.py: Report IIDs when they differ. r=ted.mielczarek.

xpcom/typelib/xpt/tools/xpt.py

@@ -1210,13 +1210,14 @@ class Typelib(object):
                         else:
                             # Same name, different IIDs, raise an exception
                             raise DataError, \
-                                  "Typelibs contain definitions of interface %s"\
-                                  " with different IIDs!" % i.name
+                                  "Typelibs contain definitions of interface %s" \
+                                    " with different IIDs (%s vs %s)!" % \
+                                    (i.name, i.iid, j.iid)
                 elif i.iid == j.iid and i.iid != Interface.UNRESOLVED_IID:
                     # Same IID, different names, raise an exception
                     raise DataError, \
-                          "Typelibs contain definitions of interface %s"\
-                          " with different names (%s vs. %s)!" %  \
+                          "Typelibs contain definitions of interface %s" \
+                            " with different names (%s vs %s)!" % \
                             (i.iid, i.name, j.name)
             if not merged:
                 # No partially matching interfaces, so just take this interface