+/**
+ * Swaps the current context to another thread of execution. This form switches
+ * from a user Thread to a system context.
+ * @param t Thread representing the current context
+ * @param ctxt Context to switch to
+ * @return Does not return, unless we return to Thread t's context. See
+ * swapcontext(3) (returns 0 for success, -1 for failure).
+ */