Partially revert PR #2190

The core shouldn't depend on constants that are not defined by itself
diff --git a/system/database/DB_cache.php b/system/database/DB_cache.php
index 0ab9c5d..b855ff2 100644
--- a/system/database/DB_cache.php
+++ b/system/database/DB_cache.php
@@ -158,12 +158,12 @@
 
 		if ( ! is_dir($dir_path))
 		{
-			if ( ! @mkdir($dir_path, DIR_WRITE_MODE))
+			if ( ! @mkdir($dir_path, 0777))
 			{
 				return FALSE;
 			}
 
-			@chmod($dir_path, DIR_WRITE_MODE);
+			@chmod($dir_path, 0777);
 		}
 
 		if (write_file($dir_path.$filename, serialize($object)) === FALSE)
@@ -171,7 +171,7 @@
 			return FALSE;
 		}
 
-		@chmod($dir_path.$filename, FILE_WRITE_MODE);
+		@chmod($dir_path.$filename, 0666);
 		return TRUE;
 	}
 
diff --git a/system/database/DB_driver.php b/system/database/DB_driver.php
index b004de3..fafce45 100644
--- a/system/database/DB_driver.php
+++ b/system/database/DB_driver.php
@@ -1676,7 +1676,7 @@
 
 		$error =& load_class('Exceptions', 'core');
 		echo $error->show_error($heading, $message, 'error_db');
-		exit(EXIT_DATABASE);
+		exit(8); // EXIT_DATABASE
 	}
 
 	// --------------------------------------------------------------------