fold -s: add option for variable spaces at beginning

[Dan Jacobson]

In case fold -s hasn't been enhanced since 5.2.1:
Unhappy with wasted spaces at the end of each line, and no variable
choice of how many spaces at the beginning of each continuation line,
$ tr \\n ' ' </etc/motd|fold -s|cat -e
$ tr \\n ' ' </etc/motd|fold -s|
perl -nwe 'BEGIN{$/=""}s/ \n/\n  /g;print'|cat -e
Here you see I decided to put two spaces at the beginning of each
continuation line, and none at the end.

Anyway, fold -s should have more option choices to enable this.