Allow custom teaser length

Hi,

I've attached a patch which allows the admin user to configure a custom teaser length for node teasers included in the email notification. This is because I didn't want to alter the default site global teaser length which appears on the website. I had to basically duplicate node_teaser() to do this, but this won't be needed in the Drupal 6 version as the D6 version of that function takes an optional teaser length setting.

The patch also includes a small fix to strip carriage returns from html emails.

Cheers,
Stella