Cannot use ticket-custom field name 'group', generates error in

[tom.cobb@…]

Small bug here, if you create a ticket-custom field with name 'group', it causes the custom query execution to fail.

extract from trac.ini:

[ticket-custom]
group = text
group.label = Group (Optional)
group.order = 2
group.value = controls

Steps to reproduce:

• Click view tickets
• Click Custom Query
• Click Update (doesn't matter what fields are in the query)

traceback:

Traceback (most recent call last):
  File "/usr/lib/python2.3/site-packages/trac/web/main.py", line 406, in dispatch_request
    dispatcher.dispatch(req)
  File "/usr/lib/python2.3/site-packages/trac/web/main.py", line 237, in dispatch
    resp = chosen_handler.process_request(req)
  File "/usr/lib/python2.3/site-packages/trac/ticket/query.py", line 414, in process_request
    req.redirect(query.get_href(req))
  File "/usr/lib/python2.3/site-packages/trac/ticket/query.py", line 189, in get_href
    format=format, **self.constraints)
TypeError: <lambda>() got multiple values for keyword argument 'group'

The problem goes away if the field is renamed to something else like 'agroup'

[cboos]

I don't think we're going to allow such special names, but what we can do is to ignore those invalid custom fields and warn the user that such custom field names are not allowed and are going to be ignored, in the line of #2431.

See #1449.