Bugfix: make custom_keywords work like described in the README

Previously you had to do this:

  [format]
  my_custom_keyword = fieldname

  [defaults]
  fieldname = default_value

Now you have to do what the README says:

  [format]
  my_custom_keyword = fieldname

  [defaults]
  my_custom_keyword = default_value

pastebinit

@@ -115,7 +115,7 @@ try:
                     elif param == 'jabberid':
                         params[paramname] = jabberid
                     else:
-                        params[paramname] = pastebind[pastebin]['defaults'][paramname]
+                        params[paramname] = pastebind[pastebin]['defaults'][param]
         if params:
             return params
         else: