Improve STANDALONE_SHELL. "safe" applets are renamed NOEXEC applets
and now this fact is recorded in applets.h, not ash.c.
Several fixes to "--help + STANDALONE_SHELL" scenarios.
function old new delta
run_current_applet_and_exit - 355 +355
arith 2064 2073 +9
refresh 1148 1156 +8
getopt32 1068 1073 +5
telnet_main 1510 1514 +4
md5_sha1_sum_main 565 566 +1
xstrtoul_range_sfx 255 251 -4
packed_usage 22523 22514 -9
tryexec 255 203 -52
static.safe_applets 152 - -152
.rodata 131320 131128 -192
run_applet_by_name 869 506 -363
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(add/remove: 1/1 grow/shrink: 5/5 up/down: 382/-772) Total: -390 bytes
./busybox ash -c 'i=20000; while test $i != 0; do touch z; i=$((i-1)); done'
runs more than twice as fast with STANDALONE_SHELL versus without.