make pw_encrypt() return malloc'ed string.

   text    data     bss     dec     hex filename
 759802     604    6684  767090   bb472 busybox_old
 759804     604    6676  767084   bb46c busybox_unstripped

diff --git a/include/libbb.h b/include/libbb.h
index bd2dbe5..655ca01 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1031,7 +1031,7 @@
  */
 extern void setup_environment(const char *shell, int clear_env, int change_env, const struct passwd *pw);
 extern int correct_password(const struct passwd *pw);
-/* Returns a ptr to static storage */
+/* Returns a malloced string */
 extern char *pw_encrypt(const char *clear, const char *salt, int cleanup);
 extern int obscure(const char *old, const char *newval, const struct passwd *pwdp);
 /* rnd is additional random input. New one is returned.