Also compiles / runs without time-based functions in OS

Can now run without need of time() / localtime() and gettimeofday()
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 4bc0fad..eca6879 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -27,8 +27,6 @@
 #ifndef POLARSSL_SSL_H
 #define POLARSSL_SSL_H
 
-#include <time.h>
-
 #include "config.h"
 #include "net.h"
 #include "bignum.h"
@@ -60,6 +58,10 @@
 #include "zlib.h"
 #endif
 
+#if defined(POLARSSL_HAVE_TIME)
+#include <time.h>
+#endif
+
 #if defined(_MSC_VER) && !defined(inline)
 #define inline _inline
 #else
@@ -306,7 +308,9 @@
  */
 struct _ssl_session
 {
+#if defined(POLARSSL_HAVE_TIME)
     time_t start;               /*!< starting time      */
+#endif
     int ciphersuite;            /*!< chosen ciphersuite */
     int compression;            /*!< chosen compression */
     size_t length;              /*!< session id length  */