*Title: Template override conditions for 'content/tipafriend.tpl' and 'content/tipafriendmail.tpl' templates.

*Documentation:
Module 'content/tipafriend' has a node id as required parameter. So it is useful
to have ability to override these templates using passed node's attributes.
From now, it is possible to use keys listed below to override 'content/tipafriend.tpl'
and 'content/tipafriendmail.tpl' templates:

object              - Matches the ID number of the object.
class               - Matches the ID number of the class which the object is an instance of.
class_identifier    - Matches the identifier of the class which the object is an instance of.
class_group         - Matches the ID number of the group that the class which the object
                      is an instance of belongs to.
section             - Matches the number of the section which the object belongs to.
node                - Matches the ID number of the node.
parent_node         - Matches the ID number of the parent node.
depth               - Matches the depth of the node. The depth of a top level node is 1.
url_alias           - Matches the virtual URL of the node.