Update Kernel#print to print $_ when no arguments are given

Author: bjfish

core/kernel/print_spec.rb

@@ -5,6 +5,18 @@
   it "is a private method" do
     Kernel.should have_private_instance_method(:print)
   end
+
+  it "delegates to $stdout" do
+    -> { print :arg }.should output("arg")
+  end
+
+  it "prints $_ when no arguments are given" do
+    orig_value = $_
+    $_ = 'foo'
+    -> { print }.should output("foo")
+  ensure
+    $_ = orig_value
+  end
 end
 
 describe "Kernel.print" do