Replaced IdentityMap.

Notes:

* Moved IdentityMap from Array to Rubinius.
* IdentityMap now supports re-mapping (#redistribute) when the entries
  exceed a certain threshhold. This happens automatically. The size is
  never reduced, however, because this is not a realistic need for the
  current use. Should this become necessary, it would be fairly simple
  to add to the #delete method as #redistribute could grow or shrink
  without any modification.
* The basic structure is a hybrid table of direct entries and rows mixed.
  On collision, the entry in the main table is promoted to a row and the
  colliding entry is added there.
* Deleting merely sets the entry for the item's hash value to nil. Under
  highly mutable loads (ie many inserts and deletes), this could lead to
  significant fragmentation. There are several ways this could be handled
  but, again, that is not in the current use cases.
* There is a slightly higher cost for small structures due to this being
  actually mutable rather than fixed. However, there is significantly
  greater performance as the load grows due to not having the spill array.
  Overall, this structure is much more robust.

kernel/common/array.rb

@@ -269,7 +269,7 @@ def &(other)
     other = Type.coerce_to other, Array, :to_ary
 
     array = []
-    im = IdentityMap.new other
+    im = Rubinius::IdentityMap.from other
 
     each { |x| array << x if im.delete x }
 
@@ -281,8 +281,7 @@ def &(other)
   def |(other)
     other = Type.coerce_to other, Array, :to_ary
 
-    im = IdentityMap.new self, other.size
-    im.load other
+    im = Rubinius::IdentityMap.from self, other
     im.to_array
   end
 
@@ -330,7 +329,7 @@ def -(other)
     other = Type.coerce_to other, Array, :to_ary
 
     array = []
-    im = IdentityMap.new other
+    im = Rubinius::IdentityMap.from other
 
     each { |x| array << x unless im.include? x }
 
@@ -1464,11 +1463,17 @@ def uniq
 
   # Removes duplicates from the Array in place as #uniq
   def uniq!
-    im = IdentityMap.new self
+    im = Rubinius::IdentityMap.from self
     return if im.size == size
 
     Ruby.check_frozen
-    im.to_array self
+
+    array = im.to_array
+    @tuple = array.tuple
+    @start = array.start
+    @total = array.total
+
+    self
   end
 
   # Returns a new Array populated from the elements in