Ghost-role arousal fix (#283)

* Ghost-role arousal fix

Fixes it so ghost role spawners respect arousal preferences of the
ghost.

* Arousal should respect species traits

This is *currently* having no effect, as no species at the time of
writing uses NOGENITALS species trait. But good for future species I
think.

* Arousal-fix-fixed

Made on_species_gain do the arousal check and apply it properly. Moved
equip to happen AFTER the ckey is assigned, as I couldn't check the
clients prefs before that and it just defaulted to TRUE.
Problem: Human ghost-roles are already human and would not use
on_species_gain. I had 2 fixes for this: Either I made them do so
anyway, doing set_species with human. This is probably redundant and
might break things in some unexpected way....
2nd possible fix is what I am pushing now, just making an else statement
for that situation.

code/modules/mob/living/carbon/human/species.dm

@@ -159,6 +159,10 @@
 		species_traits += DIGITIGRADE
 	if(DIGITIGRADE in species_traits)
 		C.Digitigrade_Leg_Swap(FALSE)
+	if(NOAROUSAL in species_traits)
+		C.canbearoused = FALSE
+	else
+		C.canbearoused = C.client.prefs.arousable
 
 /datum/species/proc/on_species_loss(mob/living/carbon/C)
 	if(C.dna.species.exotic_bloodtype)