Format: SET PROMPT prompt-type 'string'

 Where prompt-type is either LINE, KEYPAD, NOKEYPAD, HCCHANGE, INSERT,
 INSERTN, or QUERY.

 The SET PROMPT command allows redefinition of the prompt string that is
 displayed in line mode, in keypad mode, in nokeypad mode, in hardcopy
 change mode, in line mode when inserting, in line mode when inserting
 with NONUMBERS, and with the /QUERY qualifier.

 EDT will become confused if the new string for the keypad or nokeypad
 prompt causes a net motion of the cursor.  If a <CR><LF> pair is not
 included in the new string for any prompt which has it in the default
 prompt, these characters will be inserted at the beginning of the new
 string.