Fixes monkeyize/humanize removing the mob's viruses when they should be kept.

Fixes NOCLONE and CLUMSY being in both disabilities and mutations. they're now only disabilities.
Fixes minttoxin not gibbing people with the fat disabilities.
Fixes some runtimes, replacing usr by user in some places.
Fixes mutation overlays being removed when updating overlays.
Remove the now unused mob/var/list/mutations and human/var/blood_type
Fixed some formatting in preferences.dm

code/modules/mob/transform_procs.dm

@@ -59,6 +59,7 @@
 		viruses = list()
 		for(var/datum/disease/D in O.viruses)
 			D.affected_mob = O
+			D.holder = O
 
 	//keep damage?
 	if (tr_flags & TR_KEEPDAMAGE)
@@ -169,7 +170,6 @@
 	else
 		hardset_dna(O, null, null, null, null, dna.species.type)
 
-	dna = null
 	if(newname) //if there's a name as an argument, always take that one over the current name
 		O.real_name = newname
 	else
@@ -189,6 +189,7 @@
 		viruses = list()
 		for(var/datum/disease/D in O.viruses)
 			D.affected_mob = O
+			D.holder = O
 		O.med_hud_set_status()
 
 	//keep damage?