Update the TIP formatter to handle multiline tips

- includes 3 tests

railties/guides/rails_guides/textile_extensions.rb

@@ -15,10 +15,11 @@ def notestuff(body)
     end
 
     def tip(body)
-      body.gsub!(/^TIP[.:](.*)$/) do |m|
+      body.gsub!(/^TIP[.:](.*?)(\n\Z|\n\n+|\Z)/m) do |m|
         result = "<div class='info'><p>"
         result << $1.strip
         result << '</p></div>'
+        result << $2 if $2
         result
       end
     end

railties/test/guides/textile_extionsions_test.rb

@@ -0,0 +1,37 @@
+require 'isolation/abstract_unit'
+require 'guides/rails_guides/textile_extensions'
+
+class TextileExtensionsTest < Test::Unit::TestCase
+  include ActiveSupport::Testing::Isolation
+  include RailsGuides::TextileExtensions
+
+  test "tips can handle a single line" do
+    expected_output = "<div class='info'><p>this is a single line tip</p></div>"
+    assert_equal expected_output, tip('TIP. this is a single line tip')
+  end
+
+  def setup
+    @multi_line_tip = "This is a multi-line tip.\n" +
+      "Isn't it fantastic?"
+  end
+
+  test "tips can handle a multi-line tip" do
+    expected_output = "<div class='info'><p>#{@multi_line_tip}</p></div>"
+
+    assert_equal expected_output, tip("TIP. #{@multi_line_tip}")
+  end
+
+  test "muli-line tips handles text before and after the tip" do
+    pre_line = "This is text before hand.\n\n"
+    post_line = "\n\nThis is some text after"
+    input_text = pre_line +
+      "TIP. #{@multi_line_tip}" +
+      post_line
+
+    expected_output = pre_line +
+      "<div class='info'><p>#{@multi_line_tip}</p></div>" +
+      post_line
+
+    assert_equal expected_output, tip(input_text)
+  end
+end