top: use poll instead of select for waiting on one descriptor

top: use poll instead of select for waiting on one descriptor
smart_ulltoa5: make it more cryptic. -50 bytes.

function                                             old     new   delta
passwd_main                                         1095    1103      +8
getNum                                               557     565      +8
buffer_fill_and_print                                 73      76      +3
udhcpc_main                                         2393    2395      +2
mkfs_minix_main                                     3071    3070      -1
dname_enc                                            377     373      -4
expmeta                                              480     472      -8
smart_ulltoa5                                        334     283     -51
top_main                                             911     815     -96
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/5 up/down: 21/-160)          Total: -139 bytes
   text    data     bss     dec     hex filename
 770872    1063   10788  782723   bf183 busybox_old
 770732    1063   10788  782583   bf0f7 busybox_unstripped