Changes for clojure.core/conj

Alan Thompson on Thu, 13 Feb 2014
; maps and sets are treated differently
user=> (conj {1 2} {3 4})
{3 4, 1 2}   ; the contents of {3 4} are added to {1 2}

user=> (conj #{1 2} #{3})
#{1 2 #{3}}  ; the whole set #{3} is added to #{1 2}

user=> (clojure.set/union #{1 2} #{3})
#{1 2 3}  ; must use (clojure.set/union) to merge sets, not conj