libbb: password/group function helpers rewritten by Tito:

libbb: password/group function helpers rewritten by Tito:

function                                             old     new   delta
xgetpwuid                                              -      27     +27
uid2uname_utoa                                         -      22     +22
gid2group_utoa                                         -      22     +22
uid2uname                                              -      18     +18
gid2group                                              -      18     +18
buffer_fill_and_print                                179     196     +17
print_user                                            12      24     +12
print_group                                           12      24     +12
get_cached                                            89      99     +10
...
print_common                                         134     120     -14
vlock_main                                           415     396     -19
logger_main                                          410     387     -23
crontab_main                                         642     609     -33
bb_getpwuid                                           42       -     -42
bb_getgrgid                                           42       -     -42
bb_getug                                              80       -     -80
------------------------------------------------------------------------------
(add/remove: 6/3 grow/shrink: 9/11 up/down: 187/-296)        Total: -109 bytes