Do not hardcode plural values for comment nodetype

One more note. With this code format_plural() works but in an ugly way: translator is able to provide node comment plural form, but only if he ignores @comments placeholder completely, and provides single translation for all node types.
Proper way of fixing it is not letting user set plural form in UI (which is pointless because of different plural forms in different languages as I said above) but defining theme functions which user can override to provide different strings per-nodetype. Example:

function theme_nodecomments_comment_count($node, $count) {
  return format_plural($count, '1 comment', '@count comments');
}

function theme_nodecomments_new_comments($node, $count) {
  return format_plural($count, '1 new comment', '@count new comments')
}

Note that we provide sensible defaults (strings such as "1 comment" are already defined in core) but pass $node inside so user could insert $node->type checks and return different strings.

Attaching patch that implements approach described above.

Committed. http://drupal.org/cvs?commit=364950