Optimize Array.new with block.

* before
                   user     system      total        real
without block  0.280000   0.060000   0.340000 (  0.185518)
with block     0.680000   0.120000   0.800000 (  0.517797)

* after
                   user     system      total        real
without block  0.290000   0.060000   0.350000 (  0.186769)
with block     0.490000   0.040000   0.530000 (  0.394732)

{{{
require 'benchmark'

Benchmark.bm(13) do |x|
  x.report "without block" do
    1000.times do
      Array.new(10000)
    end
  end

  x.report "with block" do
    1000.times do
      Array.new(10000) {|i| }
    end
  end
end
}}}

array.c

@@ -330,6 +330,7 @@ rary_initialize(VALUE ary, SEL sel, int argc, VALUE *argv)
 
     const long len = NUM2LONG(size);
     assert_ary_len(len);
+    rary_resize(ary, len);
     if (rb_block_given_p()) {
 	if (argc == 2) {
 	    rb_warn("block supersedes default value argument");
@@ -344,7 +345,6 @@ rary_initialize(VALUE ary, SEL sel, int argc, VALUE *argv)
 	}
     }
     else {
-	rary_resize(ary, len);
 	for (long i = 0; i < len; i++) {
 	    rary_store(ary, i, val);
 	}