md5_sha1_sum: fix mishandling when run as /bin/md5sum (with path)

md5_sha1_sum: fix mishandling when run as /bin/md5sum (with path)
chown/chgrp: completely match coreutils 6.8 wrt symlink handling

function                                             old     new   delta
recursive_action                                     411     422     +11
arith                                               2033    2042      +9
collect_blk                                          467     474      +7
dhcprelay_main                                      1122    1125      +3
fsck_main                                           1909    1911      +2
singlemount                                         4555    4547      -8
xmalloc_realpath                                      14       -     -14
get_lcm                                              123     105     -18
ed_main                                             3111    3084     -27
chown_main                                           217     183     -34
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 5/4 up/down: 32/-101)           Total: -69 bytes
   text    data     bss     dec     hex filename
 684132    2744   14000  700876   ab1cc busybox_old
 684060    2744   14000  700804   ab184 busybox_unstripped