Remove warnings

* Remove assigned but not used variables (GCC 4.6)
* Bump _XOPEN_SOURCE to 600, ridding of FreeBSD warnings (this probably need
  to be tweaked on a per-implementation basis as problems arise)

src/session.c

@@ -65,6 +65,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <strings.h>
 #include <unistd.h>
 #include <time.h>