create symbols from the auto zone, allowing associative references to…

… work without emitting warnings/errors

git-svn-id: http://svn.macosforge.org/repository/ruby/MacRuby/trunk@4073 23306eb0-4c56-4727-a40e-e92c0eb68959

spec/macruby/core/symbol_spec.rb

@@ -13,4 +13,10 @@
   it "should return self on -copy" do
     :sym.copy.__id__.should == :sym.__id__
   end
+
+  it "can have instance variables attached to it" do
+    s = :foo
+    s.instance_variable_set(:@omg, 42)
+    s.instance_variable_get(:@omg).should == 42
+  end
 end

symbol.c

@@ -32,11 +32,10 @@ typedef struct {
 static rb_sym_t *
 sym_alloc(VALUE str, ID id)
 {
-    rb_sym_t *sym = (rb_sym_t *)malloc(sizeof(rb_sym_t));
+    rb_sym_t *sym = (rb_sym_t *)xmalloc(sizeof(rb_sym_t));
     assert(rb_cSymbol != 0);
     sym->klass = rb_cSymbol;
-    GC_RETAIN(str); // never released
-    sym->str = str;
+    GC_WB(&sym->str, str);
     sym->id = id;
     return sym;
 }
@@ -243,7 +242,8 @@ void
 Init_PreSymbol(void)
 {
     sym_id = CFDictionaryCreateMutable(NULL, 0, NULL, NULL);
-    id_str = CFDictionaryCreateMutable(NULL, 0, NULL, NULL);
+    id_str = CFDictionaryCreateMutable(NULL, 0, NULL,
+	    &kCFTypeDictionaryValueCallBacks);
     last_id = 1000;
 
     // Pre-register parser symbols.