ash: introduce and use stzalloc and ckzalloc.

ash: introduce and use stzalloc and ckzalloc.

function                                             old     new   delta
stzalloc                                               -      29     +29
ckzalloc                                               -      29     +29
recordregion                                         108     102      -6
cmdlookup                                            158     152      -6
pipeline                                             188     181      -7
parseheredoc                                         135     128      -7
makename                                              42      35      -7
list                                                 355     348      -7
setvareq                                             221     212      -9
aliascmd                                             324     311     -13
pushfile                                              83      69     -14
readtoken1                                          2872    2849     -23
parse_command                                       1430    1391     -39
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 0/11 up/down: 58/-138)          Total: -80 bytes
   text    data     bss     dec     hex filename
 577227     706   23740  601673   92e49 busybox_old
 577147     706   23740  601593   92df9 busybox_unstripped