Index: wp-includes/class.wp-scripts.php
===================================================================
--- wp-includes/class.wp-scripts.php	(revision 11993)
+++ wp-includes/class.wp-scripts.php	(working copy)
@@ -117,10 +117,20 @@
 		$src = add_query_arg('ver', $ver, $src);
 		$src = esc_url(apply_filters( 'script_loader_src', $src, $handle ));
 
+		$end_cond = $tag = '';
+		if ( isset($this->registered[$handle]->extra['conditional']) && $this->registered[$handle]->extra['conditional'] ) {
+			$tag .= "<!--[if {$this->registered[$handle]->extra['conditional']}]>\n";
+			$end_cond = "<![endif]-->\n";
+		}
+
+		$tag .= apply_filters( 'script_loader_tag', "<script type='text/javascript' src='$src'></script>\n", $handle );
+
+		$tag .= $end_cond;
+
 		if ( $this->do_concat )
-			$this->print_html .= "<script type='text/javascript' src='$src'></script>\n";
+			$this->print_html .= $tag;
 		else
-			echo "<script type='text/javascript' src='$src'></script>\n";
+			echo $tag;
 
 		return true;
 	}