style filter for the html part of mails didn't filter "import" and "link" style tag

[bigfaucet]

like

@import url("my.css");

or

<link href="my.css" rel="stylesheet" type="text/css" media="all" />

Maybe use frameset for showing the mail would be better, while filter the "link" and "import" tag of style statement, some style will lose. But without filtering, sometimes the whole page will be in messy format since some global style define.

[thomasb]

Fixed in trunk r839