tr: support octal ranges

tr: support octal ranges

now, we can do printf "a\tb\tcdef\n" | ./busybox tr -d "\1-\14b-e"
af

and bonus, we save some bytes.

function                                             old     new   delta
expand                                               718     699     -19
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-19)             Total: -19
bytes

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>