*Title: Enhanced filters for content/list*, content/tree*

*Documentation:
The fetch functions content/list, content/list_count, content/tree
and content/tree_count have been given extra filter functionality.

Filter attribute:
The filter attribute 'owner' has been added, this refers to the owner_id
of the content object. This can for instance be used to find all objects
of a given user.

Filter operations:
The following operations have been added.
- in, not_in: This matches the field against an array of values.
- between, not_between: This matches the field against a start and end value
  passed as an array with two elements. The field must either be part of that
  range (for between) or outside of it (for not_between).
- like, not_like: This matches the field against a wildcard string. The wildcard
  character is a *.

Example of 'owner' usage:
Fetches all objects for the current user.
{fetch( content, tree,
        hash( parent_node_id, 2,
              attribute_filter,
              array( array( 'owner', '=', $current_user.contentobject_id ) ) ) )}


Example of 'in' usage:
Fetches bugs with priority 1 and 4.
{fetch( content, tree,
        hash( parent_node_id, 2,
              attribute_filter,
              array( array( 'bug/priority', 'in', array( 1, 4 ) ) ) ) )}

Example of 'between' usage:
Fetches bugs with priority 2, 3 and 4.
{fetch( content, tree,
        hash( parent_node_id, 2,
              attribute_filter,
              array( array( 'bug/priority', 'between', array( 2, 4 ) ) ) ) )}

Example of 'like' usage:
Fetches all bugs with the text 'class' in it.
{fetch( content, tree,
        hash( parent_node_id, 2,
              attribute_filter,
              array( array( 'bug/title', 'like', '*class*' ) ) ) )}