doc: issue2551415 correct doc for change input->input_payload in 2.5 the rest interface changed a variable name from input to input_payload. An earlier commit changed the rest docs. This commit adds an item for it to the upgrading 2.4.0->2.5.0 section. Also cross reference added to the rest docs with the updated examples.

def audit_html_files(db, cl, nodeid, newvalues):
    if 'type' in newvalues and newvalues['type'] == 'text/html':
        newvalues['type'] = 'text/plain'
    

def init(db):
    db.file.audit('set', audit_html_files)
    db.file.audit('create', audit_html_files)