fphilipe/premailer-rails3 — pull request #37 by GAV1N (2012-05-23 00:02:28+00:00)
Title: Fix duplicate html_part bug when mail already has an HTML part

When the message already has an HTML part, the PremailerRails::Hook class passes a block to the message#html_part method defining a new HTML part. This method adds the new HTML part to the message, resulting in duplicate HTML parts.

I believe this:
```ruby
message.html_part do
content_type "text/html; charset=#{charset}"
body premailer.to_inline_css
end
```
Should be replaced with this:
```ruby
message.html_part do
content_type "text/html; charset=#{charset}"
body premailer.to_inline_css
end unless message.html_part
```