List fetch enhancement

*Title: List fetch enhancement

*Incentive:
Make it possible to list all children of a node allthough the current
user has no access to them.
This is quite useful if you want to list some children in a given folder
and display some information about them. If the user tries to view
the child object he will not be allowed.

*Documentation:
A new parameter has been added to content/list, content/tree,
content/list_count and content/tree_count.
- limitation - This can be set to an array containing the limitation
               information. Use an empty array for no checking and
               null for default checking. The default value is null.