fixed CRL check return value on revoked certificates

fixed possible refcounting bugs
generic return_null() implementation

src/charon/plugins/med_db/med_db_creds.c

@@ -173,14 +173,6 @@ static enumerator_t* create_shared_enumerator(private_med_db_creds_t *this,
 	}
 	return NULL;
 }
-
-/**
- * returns null
- */
-static void *return_null()
-{
-	return NULL;
-}
 	
 /**
  * Implementation of backend_t.destroy.

src/charon/plugins/sql/sql_cred.c

@@ -331,14 +331,6 @@ static enumerator_t* create_shared_enumerator(private_sql_cred_t *this,
 	return &e->public;
 }
 
-/**
- * return null
- */
-static void *return_null()
-{
-	return NULL;
-}
-
 /**
  * Implementation of sql_cred_t.destroy.
  */

src/charon/plugins/stroke/stroke.c

@@ -281,14 +281,6 @@ static void ca_section_destroy(ca_section_t *this)
 	free(this);
 }
 
-/**
- * another return NULL 
- */
-static void* return_null()
-{
-	return NULL;
-}
-
 /**
  * data to pass to create_inner_cdp
  */