MSVC compile warnings fixed.

src/plugins/mod_chat_history.c

@@ -67,7 +67,7 @@ static size_t get_messages(struct chat_history_data* data, size_t num, struct cb
 	char* message;
 	int skiplines = 0;
 	size_t lines = 0;
-	int total = list_size(messages);
+	size_t total = list_size(messages);
 
 	if (total == 0)
 		return 0;

src/system.h

@@ -270,6 +270,7 @@ typedef unsigned __int64 uint64_t;
 #define open _open
 #define close _close
 #define read _read
+#define write _write
 #define NEED_GETOPT
 #endif