fix gcc 4.7.x warnings

src/driver/pictureviewer/gif.cpp

@@ -6,6 +6,7 @@
 #ifdef FBV_SUPPORT_GIF
 	#include "pictureviewer.h"
 	#include <stdio.h>
+	#include <unistd.h>
 	#include <sys/types.h>
 	#include <sys/stat.h>
 	#include <fcntl.h>

src/driver/pictureviewer/pictureviewer.cpp

@@ -5,7 +5,7 @@
 #include "pv_config.h"
 #include "driver/framebuffer.h"
 
-
+#include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/types.h>

src/driver/shutdown_count.cpp

@@ -34,6 +34,7 @@
 
 #include <sys/timeb.h>
 #include <time.h>
+#include <unistd.h>
 
 
 SHTDCNT::SHTDCNT()