Adapt Beautifulsoup parser to changed behaviour in bs4

compressor/parser/beautifulsoup.py

@@ -34,7 +34,13 @@ class BeautifulSoupParser(ParserBase):
             return self.soup.findAll('script')
 
     def elem_attribs(self, elem):
-        return dict(elem.attrs)
+        attrs = dict(elem.attrs)
+        # hack around changed behaviour in bs4, it returns lists now instead of one string, see
+        # http://www.crummy.com/software/BeautifulSoup/bs4/doc/#multi-valued-attributes
+        for key, value in attrs.items():
+            if type(value) is list:
+                attrs[key] = " ".join(value)
+        return attrs
 
     def elem_content(self, elem):
         return elem.string