Label random-noise sources with an enum of ids.

The upcoming PRNG revamp will want to tell noise sources apart, so
that it can treat them all fairly. So I've added an extra parameter to
noise_ultralight and random_add_noise, which takes values in an
enumeration covering all the vague classes of entropy source I'm
collecting. In this commit, though, it's simply ignored.

unix/uxpgnt.c

@@ -52,7 +52,7 @@ void uxsel_input_remove(uxsel_id *id) { }
  */
 void random_save_seed(void) {}
 void random_destroy_seed(void) {}
-void noise_ultralight(unsigned long data) {}
+void noise_ultralight(NoiseSourceId id, unsigned long data) {}
 char *platform_default_s(const char *name) { return NULL; }
 bool platform_default_b(const char *name, bool def) { return def; }
 int platform_default_i(const char *name, int def) { return def; }