Include stdlib.h where its functions are used

Fixes build failure on OS X 10.10 and 10.11:

error: use of undeclared identifier 'free'
error: use of undeclared identifier 'malloc'
error: use of undeclared identifier 'qsort'

PortabilityLayer/ZipFileProxy.cpp

@@ -10,6 +10,7 @@
 #include "DeflateCodec.h"
 
 #include <algorithm>
+#include <stdlib.h>
 
 namespace
 {