Improve the 'Coercing non-XML name' warning (#418)

This can be helpful in finding the code triggering the warning.

Author: Ms2ger

html5lib/_ihatexml.py

@@ -254,15 +254,15 @@ def toXmlName(self, name):
         nameRest = name[1:]
         m = nonXmlNameFirstBMPRegexp.match(nameFirst)
         if m:
-            warnings.warn("Coercing non-XML name", DataLossWarning)
+            warnings.warn("Coercing non-XML name: %s" % name, DataLossWarning)
             nameFirstOutput = self.getReplacementCharacter(nameFirst)
         else:
             nameFirstOutput = nameFirst
 
         nameRestOutput = nameRest
         replaceChars = set(nonXmlNameBMPRegexp.findall(nameRest))
         for char in replaceChars:
-            warnings.warn("Coercing non-XML name", DataLossWarning)
+            warnings.warn("Coercing non-XML name: %s" % name, DataLossWarning)
             replacement = self.getReplacementCharacter(char)
             nameRestOutput = nameRestOutput.replace(char, replacement)
         return nameFirstOutput + nameRestOutput