Multiple newlines stripped from within MT import files

When I imported entries from my old MT blog into a new Wordpress install, I expected my multiple newlines to be preserved. This is because MT uses them to form paragraphs; the Markdown or Text Control plugins can do the same in Wordpress, but either way, if you strip them out, you get a huge bundle of text which is difficult to read.

The problem appears to be in the wp-admin/import/mt.php file, which ignores blank lines regardless of context. If a newline were added in the event of a blank line when the context was body, comment, extended or excerpt, the newlines would be preserved. The attached patch fixes this.