patch 9.0.0589: on AmigaOS4 the pid is available but the task address is used

Problem:    On AmigaOS4 the pid is available but the task address is used.
Solution:   Use getpid().  (Ola Söder, closes #11224)

src/os_amiga.c

@@ -704,7 +704,9 @@ mch_get_host_name(char_u *s, int len)
     long
 mch_get_pid(void)
 {
-#if defined(__amigaos4__) || defined(__AROS__) || defined(__MORPHOS__)
+#if defined(__amigaos4__)
+    return (long) getpid();
+#elif defined(__AROS__) || defined(__MORPHOS__)
     // This is as close to a pid as we can come. We could use CLI numbers also,
     // but then we would have two different types of process identifiers.
     return((long)FindTask(0));

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    589,
 /**/
     588,
 /**/