introduced refcounting on policy and connections

aren't stored in the IKE_SA anymore, they are queried on the fly
	are immutable now, allows it to share them
policy selection based on traffic selectors, leads to valid lookup results
	rekeying queries the policy based on its traffic selectors

src/libstrongswan/definitions.h

@@ -89,6 +89,11 @@
  */
 #define min(x,y) ((x) < (y) ? (x):(y))
 
+/**
+ * Call destructor of a object if object != NULL
+ */
+#define DESTROY_IF(obj) if (obj) obj->destroy(obj)
+
 /**
  * Debug macro to follow control flow
  */