fix gcc 4.7.x warnings

Origin commit data
------------------
Commit: 060c1c45b2
Author: Jacek Jendrzej <overx300@gmail.com>
Date: 2012-07-07 (Sat, 07 Jul 2012)

src/gui/pictureviewer.cpp

@@ -63,6 +63,7 @@
 #include <algorithm>
 #include <sys/stat.h>
 #include <sys/time.h>
+#include <unistd.h>
 
 #include <video.h>
 extern cVideo * videoDecoder;