Filters a comment form field for display.

The dynamic portion of the hook name, $name, refers to the name
of the comment form field.

Possible hook names include:

• comment_form_field_comment
• comment_form_field_author
• comment_form_field_email
• comment_form_field_url
• comment_form_field_cookies

echo apply_filters( "comment_form_field_{$name}", $field ) . "n";