Deopt Underscore methods that change on arguments

All of our currently deoptimized Underscore methods (`pick`, `omit`,
`invoke`, `without`, and `difference`) change behavior based on the
number of arguments pass to the call. This both adds `reduce` (and
friends), and explicitly deopts any method that depends on `arguments`
from falling through the cracks.

Supersedes (and incorporates) #3810.

backbone.js

@@ -68,6 +68,9 @@
   // form param named `model`.
   Backbone.emulateJSON = false;
 
+  // A cached regex to detect if the Underscore function contains the `arguments`
+  // keyword.
+  var containsArguments = /\barguments\b/;
   // Proxy Backbone class methods to Underscore functions, wrapping the model's
   // `attributes` object or collection's `models` array behind the scenes.
   //
@@ -76,6 +79,10 @@
   //
   // `Function#apply` can be slow so we use the method's arg count, if we know it.
   var addMethod = function(length, method, attribute) {
+    // In case we don't catch it, deopt Underscore functions that contain
+    // the arguments keyword.
+    if (length > 0 && containsArguments.test(_[method])) length = 0;
+
     switch (length) {
       case 1: return function() {
         return _[method](this[attribute]);
@@ -87,9 +94,6 @@
         return _[method](this[attribute], cb(iteratee, this), context);
       };
       case 4: return function(iteratee, defaultVal, context) {
-        if(arguments.length < 2) {
-          return _[method](this[attribute], cb(iteratee, this));
-        }
         return _[method](this[attribute], cb(iteratee, this), defaultVal, context);
       };
       default: return function() {
@@ -1169,8 +1173,8 @@
   // Underscore methods that we want to implement on the Collection.
   // 90% of the core usefulness of Backbone Collections is actually implemented
   // right here:
-  var collectionMethods = { forEach: 3, each: 3, map: 3, collect: 3, reduce: 4,
-      foldl: 4, inject: 4, reduceRight: 4, foldr: 4, find: 3, detect: 3, filter: 3,
+  var collectionMethods = { forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
+      foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
       select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
       contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
       head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,