use user's shell instead of hardwired "/bin/sh" (android needs this)

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

include/libbb.h

@@ -1198,10 +1198,17 @@ char *bb_simplify_path(const char *path) FAST_FUNC;
 /* Returns ptr to NUL */
 char *bb_simplify_abs_path_inplace(char *path) FAST_FUNC;
 
-#define FAIL_DELAY 3
+#define LOGIN_FAIL_DELAY 3
 extern void bb_do_delay(int seconds) FAST_FUNC;
 extern void change_identity(const struct passwd *pw) FAST_FUNC;
 extern void run_shell(const char *shell, int loginshell, const char *command, const char **additional_args) NORETURN FAST_FUNC;
+
+/* Returns $SHELL, getpwuid(getuid())->pw_shell, or DEFAULT_SHELL.
+ * Note that getpwuid result might need xstrdup'ing
+ * if there is a possibility of intervening getpwxxx() calls.
+ */
+const char *get_shell_name(void);
+
 #if ENABLE_SELINUX
 extern void renew_current_security_context(void) FAST_FUNC;
 extern void set_current_security_context(security_context_t sid) FAST_FUNC;