more robust node_submit()

when a user with administer nodes perm submits a node, the status and promote and similar attributes are taken from the $_POST. Other users have those values set for them according to the content type settings. Thats all fine, but sometimes nodes get created outside of the node form such as via email into mailhandler. Mailhandler submits the node using the API provided by node.module (i.e. call node_submit() then node_save()). This works poorly when the submitter hasd the admin nodes perm because no status, sticky, promote values are supplied and node_submit() assumes they are all false. Instead, it should assume the content type defaults. this can be achieved by always treating the incomimg post as if it were authored by a usual user and then overriding any values supplied by an 'administer nodes' user.