more: fix ARROW_DOWN and PAGE_DOWN behaviour to not skip lines

more: fix ARROW_DOWN and PAGE_DOWN behaviour to not skip lines

Currently ARROW_DOWN and PAGE_DOWN is bound to command 's' (skip lines).
But this behaviour is not what the user expects, since at least one line
is always missing! Furthermore at the end of the file there is typically
this skipping lines message, if the remainder does not fit in a
complete screen. This conflicts also with e.g. less and man PAGE_DOWN
behaviour. The 'natural' behaviour is binding to
more_kc_jump_lines_per_screen.
If more is extended to also jump only a specific number of lines forward,
this would be even a better binding for ARROW_DOWN.