ordering: deprecate the order keyword for ordering-related functions.

Author: StefanKarpinski

base/ordering.jl

@@ -78,6 +78,8 @@ ordtype   (o::By,              vs::AbstractArray) = try typeof(o.by(vs[1])) catc
 ordtype{T}(o::Ordering,        vs::AbstractArray{T}) = T
 
 function ord(lt::Function, by::Function, rev::Bool, order::Ordering=Forward)
+    order == Forward ||
+        Base.warn_once("the `order` keyword is deprecated, use `lt`, `by` and `rev` instead.")
     o = (lt===isless) & (by===identity) ? order  :
         (lt===isless) & (by!==identity) ? By(by) :
         (lt!==isless) & (by===identity) ? Lt(lt) :