Update system/core/Log.php

Updated Log.php so that a developer can extend it and change the log file extension.

It makes sense to default to .php when logs are in the public web folder.  It would be nice if a developer moves the log file path we have the option to use a standard extension like .log
diff --git a/system/core/Log.php b/system/core/Log.php
index f5d091e..3b0a921 100644
--- a/system/core/Log.php
+++ b/system/core/Log.php
@@ -71,6 +71,13 @@
 	 * @var string
 	 */
 	protected $_date_fmt		= 'Y-m-d H:i:s';
+	
+	/**
+	 * Log file extension
+	 *
+	 * @var string
+	 */
+	protected $_log_ext		= 'php';
 
 	/**
 	 * Whether or not the logger can write to the log files
@@ -147,7 +154,7 @@
 			return FALSE;
 		}
 
-		$filepath = $this->_log_path.'log-'.date('Y-m-d').'.php';
+		$filepath = $this->_log_path.'log-'.date('Y-m-d').'.'.$this->_log_ext;
 		$message  = '';
 
 		if ( ! file_exists($filepath))
@@ -179,4 +186,4 @@
 }
 
 /* End of file Log.php */
-/* Location: ./system/core/Log.php */
\ No newline at end of file
+/* Location: ./system/core/Log.php */