CLJ-1414: sort and sort-by promise stable sort in their doc strings

Signed-off-by: Stuart Halloway <stu@cognitect.com>

Author: jafingerhut

src/clj/clojure/core.clj

@@ -2986,8 +2986,9 @@
 (defn sort
   "Returns a sorted sequence of the items in coll. If no comparator is
   supplied, uses compare.  comparator must implement
-  java.util.Comparator.  If coll is a Java array, it will be modified.
-  To avoid this, sort a copy of the array."
+  java.util.Comparator.  Guaranteed to be stable: equal elements will
+  not be reordered.  If coll is a Java array, it will be modified.  To
+  avoid this, sort a copy of the array."
   {:added "1.0"
    :static true}
   ([coll]
@@ -3003,8 +3004,9 @@
   "Returns a sorted sequence of the items in coll, where the sort
   order is determined by comparing (keyfn item).  If no comparator is
   supplied, uses compare.  comparator must implement
-  java.util.Comparator.  If coll is a Java array, it will be modified.
-  To avoid this, sort a copy of the array."
+  java.util.Comparator.  Guaranteed to be stable: equal elements will
+  not be reordered.  If coll is a Java array, it will be modified.  To
+  avoid this, sort a copy of the array."
   {:added "1.0"
    :static true}
   ([keyfn coll]