bug#7574: [PATCH]: echo, printf, stat: Allow only up to 8 bit octal input for backslash-escaped chars

[Paul Eggert]

As a minor point, both uses like this:

'4' <= *p && *p <= '7'

can be replaced with something like this:

'4' <= *p

and similarly, this:

'0' <= c && c <= '3'

can be replaced with this:

c < '4'

The replacements are not only shorter, but easier
to understand, because otherwise the reader is left
wondering why that unnecessary comparison to '7'
(or '0') is in there.