PersistentHashMap ported from Clojure

In addition to the PHM implementation, this commit introduces two new
bit ops, bit-shift-right-zero-fill (with accompanying compiler macro)
and bit-count.

An internal general purpose coercive-= compiler macro and two special
purpose internal compiler macros mask and bitpos are also introduced.

INode operations are implemented directly on the node objects (via
Object in deftype).

cljs.core/hash-map and compiler's emit :map now use PersistentHashMap,
so maps and sets are now persistent by default.

ObjMap and HashMap are now marked deprecated.

src/clj/cljs/compiler.clj

@@ -343,18 +343,11 @@
 (defmethod emit :map
   [{:keys [children env simple-keys? keys vals]}]
   (emit-wrap env
-    (if simple-keys?
-      (emits "cljs.core.ObjMap.fromObject(["
-             (comma-sep keys) ; keys
-             "],{"
-             (comma-sep (map (fn [k v] #(emits k ":" v))
-                             keys vals)) ; js obj
-             "})")
-      (emits "cljs.core.HashMap.fromArrays(["
-             (comma-sep keys)
-             "],["
-             (comma-sep vals)
-             "])"))))
+    (emits "cljs.core.PersistentHashMap.fromArrays(["
+           (comma-sep keys)
+           "],["
+           (comma-sep vals)
+           "])")))
 
 (defmethod emit :vector
   [{:keys [children env]}]

src/clj/cljs/core.clj

@@ -52,6 +52,10 @@
 (defmacro coercive-not= [x y]
   (bool-expr (list 'js* "(~{} != ~{})" x y)))
 
+;; internal - do not use.
+(defmacro coercive-= [x y]
+  (bool-expr (list 'js* "(~{} == ~{})" x y)))
+
 (defmacro true? [x]
   (bool-expr (list 'js* "~{} === true" x)))
 
@@ -183,9 +187,20 @@
 (defmacro bit-shift-right [x n]
   (list 'js* "(~{} >> ~{})" x n))
 
+(defmacro bit-shift-right-zero-fill [x n]
+  (list 'js* "(~{} >>> ~{})" x n))
+
 (defmacro bit-set [x n]
   (list 'js* "(~{} | (1 << ~{}))" x n))
 
+;; internal
+(defmacro mask [hash shift]
+  (list 'js* "((~{} >>> ~{}) & 0x01f)" hash shift))
+
+;; internal
+(defmacro bitpos [hash shift]
+  (list 'js* "(1 << ~{})" `(mask ~hash ~shift)))
+
 (defn- protocol-prefix [psym]
   (str (.replace (str psym) \. \$) "$"))