shuf: new applet

function                                             old     new   delta
shuf_main                                              -     478    +478
packed_usage                                       29571   29719    +148
applet_names                                        2460    2465      +5
applet_main                                         1428    1432      +4
applet_nameofs                                       714     716      +2
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 4/0 up/down: 637/0)             Total: 637 bytes

Based on the code by Bartosz Golaszewski <bartekgola@gmail.com>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
use [s]rand(), not [s]random()

rand() is the most standard C library function,
and on uclibc they are the same. I guess
they are the same in most todays' libc...

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>