Initial Async notify code changes

Initial API implemented for notifying applications that an ASYNC_JOB
has completed. Currently only s_server is using this. The Dummy Async
engine "cheats" in that it notifies that it has completed *before* it
pauses the job. A normal async engine would not do that.

Only the posix version of this has been implemented so far, so it will
probably fail to compile on Windows at the moment.

Reviewed-by: Rich Salz <rsalz@openssl.org>

crypto/async/async_locl.h

@@ -70,6 +70,9 @@ struct async_job_st {
     void *funcargs;
     int ret;
     int status;
+    int wake_set;
+    int wait_fd;
+    int wake_fd;
 };
 
 void ASYNC_start_func(void);