Adds ghost click to posibrains.

Added ghost trap system used by plants and posibrains to get players. Added attack_ghost() to hydro trays and posibrains for the aforementioned.
Changelog.
Minor typo.
Topic fixes.
Minor fix.

code/modules/ghosttrap/trap.dm

@@ -0,0 +1,114 @@
+// This system is used to grab a ghost from observers with the required preferences and
+// lack of bans set. See posibrain.dm for an example of how they are called/used. ~Z
+
+var/list/ghost_traps
+
+proc/get_ghost_trap(var/trap_key)
+	if(!ghost_traps)
+		populate_ghost_traps()
+	return ghost_traps[trap_key]
+
+proc/populate_ghost_traps()
+	ghost_traps = list()
+	for(var/traptype in typesof(/datum/ghosttrap))
+		var/datum/ghosttrap/G = new traptype
+		ghost_traps[G.object] = G
+
+/datum/ghosttrap
+	var/object = "positronic brain"
+	var/list/ban_checks = list("AI","Cyborg")
+	var/pref_check = BE_AI
+	var/ghost_trap_message = "They are occupying a positronic brain now."
+	var/ghost_trap_role = "Positronic Brain"
+
+// Check for bans, proper atom types, etc.
+/datum/ghosttrap/proc/assess_candidate(var/mob/dead/observer/candidate)
+	if(!istype(candidate) || !candidate.client || !candidate.ckey)
+		return 0
+	if(!candidate.MayRespawn())
+		candidate << "You have made use of the AntagHUD and hence cannot enter play as \a [object]."
+		return 0
+	if(islist(ban_checks))
+		for(var/bantype in ban_checks)
+			if(jobban_isbanned(candidate, "[bantype]"))
+				candidate << "You are banned from one or more required roles and hence cannot enter play as \a [object]."
+				return 0
+	return 1
+
+// Print a message to all ghosts with the right prefs/lack of bans.
+/datum/ghosttrap/proc/request_player(var/mob/target, var/request_string)
+	if(!target)
+		return
+	for(var/mob/dead/observer/O in player_list)
+		if(!O.MayRespawn())
+			continue
+		if(islist(ban_checks))
+			for(var/bantype in ban_checks)
+				if(jobban_isbanned(O, "[bantype]"))
+					continue
+		if(pref_check && !(O.client.prefs.be_special & pref_check))
+			continue
+		if(O.client)
+			O << "[request_string]<a href='?src=\ref[src];candidate=\ref[O];target=\ref[target]'>Click here</a> if you wish to play as this option."
+
+// Handles a response to request_player().
+/datum/ghosttrap/Topic(href, href_list)
+	if(..())
+		return 1
+	if(href_list["candidate"] && href_list["target"])
+		var/mob/dead/observer/candidate = locate(href_list["candidate"]) // BYOND magic.
+		var/mob/target = locate(href_list["target"])                     // So much BYOND magic.
+		if(!target || !candidate)
+			return
+		if(candidate == usr && assess_candidate(candidate) && !target.ckey)
+			transfer_personality(candidate,target)
+		return 1
+
+// Shunts the ckey/mind into the target mob.
+/datum/ghosttrap/proc/transfer_personality(var/mob/candidate, var/mob/target)
+	if(!assess_candidate(candidate))
+		return 0
+	target.ckey = candidate.ckey
+	if(target.mind)
+		target.mind.assigned_role = "[ghost_trap_role]"
+	announce_ghost_joinleave(candidate, 0, "[ghost_trap_message]")
+	welcome_candidate(target)
+	set_new_name(target)
+	return 1
+
+// Fluff!
+/datum/ghosttrap/proc/welcome_candidate(var/mob/target)
+	target << "<b>You are a positronic brain, brought into existence on [station_name()].</b>"
+	target << "<b>As a synthetic intelligence, you answer to all crewmembers, as well as the AI.</b>"
+	target << "<b>Remember, the purpose of your existence is to serve the crew and the station. Above all else, do no harm.</b>"
+	target << "<b>Use say :b to speak to other artificial intelligences.</b>"
+	var/turf/T = get_turf(target)
+	T.visible_message("<span class='notice'>\The [src] chimes quietly.</span>")
+	var/obj/item/device/mmi/digital/posibrain/P = target.loc
+	if(!istype(P)) //wat
+		return
+	P.searching = 0
+	P.name = "positronic brain ([P.brainmob.name])"
+	P.icon_state = "posibrain-occupied"
+
+// Allows people to set their own name. May or may not need to be removed for posibrains if people are dumbasses.
+/datum/ghosttrap/proc/set_new_name(var/mob/target)
+	var/newname = sanitizeSafe(input(target,"Enter a name, or leave blank for the default name.", "Name change","") as text, MAX_NAME_LEN)
+	if (newname != "")
+		target.real_name = newname
+		target.name = target.real_name
+
+// Doona pods and walking mushrooms.
+/datum/ghosttrap/plant
+	object = "living plant"
+	ban_checks = list("Dionaea")
+	pref_check = BE_PLANT
+	ghost_trap_message = "They are occupying a living plant now."
+	ghost_trap_role = "Plant"
+
+/datum/ghosttrap/plant/welcome_candidate(var/mob/target)
+	target << "<span class='alium><B>You awaken slowly, stirring into sluggish motion as the air caresses you.</B></span>"
+	// This is a hack, replace with some kind of species blurb proc.
+	if(istype(host,/mob/living/carbon/alien/diona))
+		target << "<B>You are \a [target], one of a race of drifting interstellar plantlike creatures that sometimes share their seeds with human traders.</B>"
+		target << "<B>Too much darkness will send you into shock and starve you, but light will help you heal.</B>"