Support for git config --global gist.private yes

I don't want gisters to accidentally create public gists of stuff that
they thought would be private.

bin/gist

@@ -120,7 +120,7 @@ begin
                        :html_url
                      end
 
-  options[:public] = !options.delete(:private)
+  options[:public] = Gist.should_be_public?(options)
 
   if options[:paste]
     puts Gist.gist(Gist.paste, options)

lib/gist.rb

@@ -343,4 +343,13 @@ def auth_token_file
       File.expand_path "~/.gist"
     end
   end
+
+  def legacy_private_gister?
+    return unless which('git')
+    `git config --global gist.private` =~ /\Ayes|1|true|on\z/i
+  end
+
+  def should_be_public?(options={})
+    !(options[:private] || Gist.legacy_private_gister?)
+  end
 end

spec/gist_spec.rb

@@ -0,0 +1,18 @@
+describe Gist do
+
+  describe "should_be_public?" do
+    it "should return false if -p is specified" do
+      Gist.should_be_public?(private: true).should be_false
+    end
+
+    it "should return false if legacy_private_gister?" do
+      Gist.should_receive(:legacy_private_gister?).and_return(true)
+      Gist.should_be_public?.should be_false
+    end
+
+    it "should return true by default" do
+      Gist.should_be_public?.should be_true
+    end
+  end
+
+end