[core thread]

* added thread_getlastpid() to header

core/include/thread.h

@@ -62,6 +62,12 @@ int thread_wakeup(int pid);
  */
 int thread_getpid();
 
+/**
+ * @brief   Returns the process ID of the thread running before the current one.
+ * @return  Obviously you are not a golfer.
+ */
+int thread_getlastpid();
+
 /**
  * @brief Measures the stack usage of a stack.
  * Only works if the thread was created with the flag CREATE_STACKTEST.