Rename conflicting ActionMailer::MailHelper#simple_format method

This was conflicting with ActionView::Helpers::TextHelper#simple_format
from within email templates.

actionmailer/lib/action_mailer/mail_helper.rb

@@ -4,7 +4,7 @@ module ActionMailer
     # each line, and wrapped at 72 columns.
     def block_format(text)
       formatted = text.split(/\n\r\n/).collect { |paragraph|
-        simple_format(paragraph)
+        format_paragraph(paragraph)
       }.join("\n")
 
       # Make list points stand on their own line
@@ -30,7 +30,7 @@ module ActionMailer
     end
 
     private
-    def simple_format(text, len = 72, indent = 2)
+    def format_paragraph(text, len = 72, indent = 2)
       sentences = [[]]
 
       text.split.each do |word|