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

diff --git a/include/libbb.h b/include/libbb.h
index e4ccc75..acae93a 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -702,14 +702,14 @@
 void xget_uidgid(struct bb_uidgid_t*, const char*) FAST_FUNC;
 /* chown-like handling of "user[:[group]" */
 void parse_chown_usergroup_or_die(struct bb_uidgid_t *u, char *user_group) FAST_FUNC;
-/* bb_getpwuid, bb_getgrgid:
- * bb_getXXXid(buf, bufsz, id) - copy user/group name or id
- *              as a string to buf, return user/group name or NULL
- * bb_getXXXid(NULL, 0, id) - return user/group name or NULL
- * bb_getXXXid(NULL, -1, id) - return user/group name or exit
-*/
-char *bb_getpwuid(char *name, int bufsize, long uid) FAST_FUNC;
-char *bb_getgrgid(char *group, int bufsize, long gid) FAST_FUNC;
+struct passwd* xgetpwuid(uid_t uid) FAST_FUNC;
+struct group* xgetgrgid(gid_t gid) FAST_FUNC;
+char* xuid2uname(uid_t uid) FAST_FUNC;
+char* xgid2group(gid_t gid) FAST_FUNC;
+char* uid2uname(uid_t uid) FAST_FUNC;
+char* gid2group(gid_t gid) FAST_FUNC;
+char* uid2uname_utoa(long uid) FAST_FUNC;
+char* gid2group_utoa(long gid) FAST_FUNC;
 /* versions which cache results (useful for ps, ls etc) */
 const char* get_cached_username(uid_t uid) FAST_FUNC;
 const char* get_cached_groupname(gid_t gid) FAST_FUNC;