Some more rebranding for consistency's sake

src/common/plugin-timer.h

@@ -1,5 +1,5 @@
-#ifndef XCHAT_PLUGIN_TIMER_H
-#define XCHAT_PLUGIN_TIMER_H
+#ifndef HEXCHAT_PLUGIN_TIMER_H
+#define HEXCHAT_PLUGIN_TIMER_H
 
 int timer_plugin_init (xchat_plugin *plugin_handle, char **plugin_name,
 				char **plugin_desc, char **plugin_version, char *arg);