Ingore color codes etc when reading buffer
Don't rewind unecessarily far in history when looking for rdb prompt
For me, comit-last-input-end was negative

(Not sure why - cargo-culted change...)
Adjust the line number we've found by one

Not sure why, but the marker was being placed one line too late in the
source code
Replace regex to mark rdb source line identifier.

Didn't understand the existing one - why would it have ^Z there?