remove apache-specific x-sendfile stuff

implement a hook (HOOK_SEND_LOCAL_FILE) which plugins may use to send files
via httpd-specific implementation to increase performance typically on larger files

include/functions.php

@@ -2514,3 +2514,33 @@
 		}
 	}
 
+	/*	this is essentially a wrapper for readfile() which allows plugins to hook
+		output with httpd-specific "fast" implementation i.e. X-Sendfile or whatever else
+
+		hook function should return true if request was handled (or at least attempted to)
+
+		note that this can be called without user context so the plugin to handle this
+		should be loaded systemwide in config.php */
+	function send_local_file($filename) {
+		if (file_exists($filename)) {
+			$tmppluginhost = new PluginHost();
+
+			$tmppluginhost->load(PLUGINS, PluginHost::KIND_SYSTEM);
+			$tmppluginhost->load_data();
+
+			foreach ($tmppluginhost->get_hooks(PluginHost::HOOK_SEND_LOCAL_FILE) as $plugin) {
+				if ($plugin->hook_send_local_file($filename)) return true;
+			}
+
+			$mimetype = mime_content_type($filename);
+			header("Content-type: $mimetype");
+
+			$stamp = gmdate("D, d M Y H:i:s", filemtime($filename)) . " GMT";
+			header("Last-Modified: $stamp", true);
+
+			return readfile($filename);
+		} else {
+			return false;
+		}
+	}
+