Convert a position to a row/column coordinate or the other way around.
Data String: 2 bytes, 1st byte session ID, or blank for current session. Byte 2 is "P" to convert position to a row/column or "R" to go from row/column to position.
Data Length: When type is "R", the row number (base is 1..numrows)
PS Position: When type is "R", column number; when type is "P", the position on screen (1..number of positions)
Returns
Data Length: When type is "P", the row number of the position. When type is "R", a zero is returned to indicate an invalid row was passed (less than zero or above the number of active rows on the screen).
RetCode: WHLLOK -- column number bad, otherwise, if type is "P" column number, if type is "R", the returned position.
