*: s/"/bin/sh"/DEFAULT_SHELL, run_shell() API fix, remove unneeded strdup

function                                             old     new   delta
run_shell                                            157     166      +9
su_main                                              477     470      -7
sulogin_main                                         515     503     -12

Signed-off-by: Ladislav Michl <Ladislav.Michl@seznam.cz>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/archival/libunarchive/data_extract_to_command.c b/archival/libunarchive/data_extract_to_command.c
index 53a7217..eb09439 100644
--- a/archival/libunarchive/data_extract_to_command.c
+++ b/archival/libunarchive/data_extract_to_command.c
@@ -102,8 +102,8 @@
 			close(p[1]);
 			xdup2(p[0], STDIN_FILENO);
 			signal(SIGPIPE, SIG_DFL);
-			execl("/bin/sh", "/bin/sh" + 5, "-c", archive_handle->tar__to_command, NULL);
-			bb_perror_msg_and_die("can't execute '%s'", "/bin/sh");
+			execl(DEFAULT_SHELL, DEFAULT_SHELL_SHORT_NAME, "-c", archive_handle->tar__to_command, NULL);
+			bb_perror_msg_and_die("can't execute '%s'", DEFAULT_SHELL);
 		}
 		close(p[0]);
 		/* Our caller is expected to do signal(SIGPIPE, SIG_IGN)