Index: wp-includes/functions.wp-scripts.php
===================================================================
--- wp-includes/functions.wp-scripts.php	(revision 22265)
+++ wp-includes/functions.wp-scripts.php	(working copy)
@@ -183,3 +183,15 @@
 
 	return (bool) $wp_scripts->query( $handle, $list );
 }
+
+function wp_script_add_data( $handle, $key, $value ){
+	global $wp_scripts;
+	if ( ! is_a( $wp_scripts, 'WP_Scripts' ) ) {
+		if ( ! did_action( 'init' ) )
+			_doing_it_wrong( __FUNCTION__, sprintf( __( 'Scripts and styles should not be registered or enqueued until the %1$s, %2$s, or %3$s hooks.' ),
+				'<code>wp_enqueue_scripts</code>', '<code>admin_enqueue_scripts</code>', '<code>init</code>' ), '3.5' );
+		$wp_scripts = new WP_Scripts();
+	}
+
+	return (bool) $wp_scripts->add_data( $handle, $key, $value );
+}
Index: wp-includes/functions.wp-styles.php
===================================================================
--- wp-includes/functions.wp-styles.php	(revision 22265)
+++ wp-includes/functions.wp-styles.php	(working copy)
@@ -190,3 +190,15 @@
 
 	return (bool) $wp_styles->query( $handle, $list );
 }
+
+function wp_style_add_data( $handle, $key, $value ){
+	global $wp_styles;
+	if ( ! is_a( $wp_styles, 'WP_Styles' ) ) {
+		if ( ! did_action( 'init' ) )
+			_doing_it_wrong( __FUNCTION__, sprintf( __( 'Scripts and styles should not be registered or enqueued until the %1$s, %2$s, or %3$s hooks.' ),
+				'<code>wp_enqueue_scripts</code>', '<code>admin_enqueue_scripts</code>', '<code>init</code>' ), '3.5' );
+		$wp_styles = new WP_Styles();
+	}
+
+	return (bool) $wp_styles->add_data( $handle, $key, $value );
+}
Index: wp-includes/class.wp-scripts.php
===================================================================
--- wp-includes/class.wp-scripts.php	(revision 22265)
+++ wp-includes/class.wp-scripts.php	(working copy)
@@ -83,22 +83,24 @@
 			return false;
 		}
 
+		$obj = $this->registered[$handle];
+
 		if ( false === $group && in_array($handle, $this->in_footer, true) )
 			$this->in_footer = array_diff( $this->in_footer, (array) $handle );
 
-		if ( null === $this->registered[$handle]->ver )
+		if ( null === $obj->ver )
 			$ver = '';
 		else
-			$ver = $this->registered[$handle]->ver ? $this->registered[$handle]->ver : $this->default_version;
+			$ver = $obj->ver ? $obj->ver : $this->default_version;
 
 		if ( isset($this->args[$handle]) )
 			$ver = $ver ? $ver . '&amp;' . $this->args[$handle] : $this->args[$handle];
 
-		$src = $this->registered[$handle]->src;
+		$src = $obj->src;
 
 		if ( $this->do_concat ) {
 			$srce = apply_filters( 'script_loader_src', $src, $handle );
-			if ( $this->in_default_dir($srce) ) {
+			if ( $this->in_default_dir($srce) && ! isset( $obj->extra['conditional'] ) ) {
 				$this->print_code .= $this->print_extra_script( $handle, false );
 				$this->concat .= "$handle,";
 				$this->concat_version .= "$handle$ver";
@@ -119,10 +121,16 @@
 
 		$src = esc_url( apply_filters( 'script_loader_src', $src, $handle ) );
 
+		$cond_before = $cond_after = null;
+		if ( isset($obj->extra['conditional']) && $obj->extra['conditional'] ) {
+			$cond_before = "<!--[if {$obj->extra['conditional']}]>\n";
+			$cond_after = "<![endif]-->\n";
+		}
+
 		if ( $this->do_concat )
-			$this->print_html .= "<script type='text/javascript' src='$src'></script>\n";
+			$this->print_html .= "$cond_before<script type='text/javascript' src='$src'></script>\n$cond_after";
 		else
-			echo "<script type='text/javascript' src='$src'></script>\n";
+			echo "$cond_before<script type='text/javascript' src='$src'></script>\n$cond_after";
 
 		return true;
 	}