fixed incompatibility with spreadsheet.py

gluon/contrib/spreadsheet.py

@@ -855,9 +855,9 @@ class Sheet:
 
             sorted_headers = [TH(),] + \
             [TH(header[1]) for header in sorted(unsorted_headers)]
-            table.insert(0, TR(*sorted_headers, _class="%s_fieldnames" % \
-                               attributes["_class"]))
-
+            table.insert(0, TR(*sorted_headers, 
+                                **{_class:"%s_fieldnames" % \
+                                       attributes["_class"]}))
         else:
             data = SCRIPT(""" // web2py Spreadsheets: no db data.""")