output-lua: add file callbacks

output-lua: add file callbacks

SCFileInfo: returns fileid (number), txid (number), name (string),
            size (number), magic (string), md5 in hex (string)

Example:

    function log(args)
        fileid, txid, name, size, magic, md5 = SCFileInfo()

SCFileState: returns state (string), stored (bool)

Example:
    function log(args)
        state, stored = SCFileState()