io_read_text and io_write_text

The database structures typically contain record numbers of text strings rather than copies of the strings themselves, as this easily allows resizing of the strings.

io_read_text io record_number

Reads the text from record_number and returns it. Results in a Tcl error if it fails.

io_write_text io record_number text

Writes text to the requested record_number. Returns 0 for success, -1 for failure