(macro) replay one or more instructions

REPLAY     -- replay all instructions in the current session
              (i.e., state-stack)
(REPLAY 5) -- replay the most recent 5 instructions
        (COMMENT deleted dive command here))
           -- replace the 5th most recent instruction with the
              indicated comment instruction, and then replay it
              followed by the remaining 4 instructions

General Form:
(REPLAY &OPTIONAL n replacement-instruction)
Replay the last n instructions if n is a positive integer; else n should be nil or not supplied, and replay all instructions. However, if replacement-instruction is supplied and not nil, then before the replay, replace the nth instruction (from the most recent, as shown by commands) with replacement-instruction.

If this command ``fails'', then the restore command will revert the state-stack to its value present before the replay instruction was executed.