hush: add showvar command for hush shell.

This new command shows the local variables defined in
the hush shell:

=> help showvar
showvar
    - print values of all hushshell variables
showvar name ...
    - print value of hushshell variable 'name'

Also make the set_local_var() and unset_local_var ()
no longer static, so it is possible to define local
hush shell variables at boot time. If CONFIG_HUSH_INIT_VAR
is defined, u-boot calls hush_init_var (), where
boardspecific code can define local hush shell
variables at boottime.

Signed-off-by: Heiko Schocher <hs@denx.de>

common/main.c

@@ -341,6 +341,10 @@ void main_loop (void)
 	u_boot_hush_start ();
 #endif
 
+#if defined(CONFIG_HUSH_INIT_VAR)
+	hush_init_var ();
+#endif
+
 #ifdef CONFIG_AUTO_COMPLETE
 	install_auto_complete();
 #endif