Improve inline documentation for the wpdb::$show_errors property.

Note that SQL/DB errors are displayed by default if both WP_DEBUG and WP_DEBUG_DISPLAY evaluate to true.

Props ericlewis.
Fixes #16615.

Built from https://develop.svn.wordpress.org/trunk@28243


git-svn-id: http://core.svn.wordpress.org/trunk@28071 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/wp-db.php

@@ -52,7 +52,10 @@ define( 'ARRAY_N', 'ARRAY_N' );
 class wpdb {
 
 	/**
-	 * Whether to show SQL/DB errors
+	 * Whether to show SQL/DB errors.
+	 *
+	 * Default behavior is to show errors if both WP_DEBUG and WP_DEBUG_DISPLAY
+	 * evaluated to true.
 	 *
 	 * @since 0.71
 	 * @access private