ash: a bunch of trivial simplifications

ash: a bunch of trivial simplifications

Also, in a few places made code more reliable wrt large sizeof(int)
and sizeof(arith_t)..

function                                             old     new   delta
sprint_status48                                        -     143    +143
newline_and_flush                                      -      56     +56
showjob                                              365     382     +17
parse_command                                       1440    1443      +3
cmdputs                                              334     332      -2
cmdloop                                              434     429      -5
showjobs                                              70      64      -6
fg_bgcmd                                             296     290      -6
ash_vmsg                                             159     153      -6
ash_main                                            1487    1481      -6
jobscmd                                               94      82     -12
getoptscmd                                           687     632     -55
outcslow                                              56       -     -56
sprint_status                                        156       -    -156
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 2/8 up/down: 219/-310)          Total: -91 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>