ash/hush: provide help text

$ ./busybox ash --help
BusyBox v1.19.0.git (2011-03-07 11:25:29 CET) multi-call binary.

Usage: ash [-/+OPTCHARS] [-/+o OPTNAME]... [-c 'SCRIPT' [ARG0 [ARGS]] / SCRIPT_FILE [ARGS]]

Unix shell interpreter

$ ./busybox hush --help
BusyBox v1.19.0.git (2011-03-07 11:25:29 CET) multi-call binary.

Usage: hush [-nx] [-c 'SCRIPT' [ARG0 [ARGS]] / SCRIPT_FILE [ARGS]]

Unix shell interpreter

function                                             old     new   delta
packed_usage                                       28163   28212     +49
setcmd                                                85      78      -7
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 49/-7)              Total: 42 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush.c b/shell/hush.c
index 4d9e5f8..6b3dc46 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -255,14 +255,21 @@
  * therefore we don't show them either.
  */
 //usage:#define hush_trivial_usage
-//usage:       "[-nx] [-c SCRIPT]"
-//usage:#define hush_full_usage ""
+//usage:	"[-nx] [-c 'SCRIPT' [ARG0 [ARGS]] / SCRIPT_FILE [ARGS]]"
+//usage:#define hush_full_usage "\n\n"
+//usage:	"Unix shell interpreter"
+
 //usage:#define msh_trivial_usage hush_trivial_usage
-//usage:#define msh_full_usage ""
-//usage:#define sh_trivial_usage NOUSAGE_STR
-//usage:#define sh_full_usage ""
-//usage:#define bash_trivial_usage NOUSAGE_STR
-//usage:#define bash_full_usage ""
+//usage:#define msh_full_usage hush_full_usage
+
+//usage:#if ENABLE_FEATURE_SH_IS_HUSH
+//usage:# define sh_trivial_usage hush_trivial_usage
+//usage:# define sh_full_usage    hush_full_usage
+//usage:#endif
+//usage:#if ENABLE_FEATURE_BASH_IS_HUSH
+//usage:# define bash_trivial_usage hush_trivial_usage
+//usage:# define bash_full_usage    hush_full_usage
+//usage:#endif
 
 
 /* Build knobs */