POSIX Asynchronous I/O support: other files

Updates to misc files to integrate AIO into the Cygwin source tree.
Much of it has to be done when adding any new syscalls.  There are
some updates to limits.h for AIO-specific limits.  And some doc mods.

winsup/cygwin/thread.cc

@@ -663,7 +663,7 @@ pthread::cancel ()
    Required cancellation points:
 
     * accept ()
-    o aio_suspend ()
+    * aio_suspend ()
     * clock_nanosleep ()
     * close ()
     * connect ()
@@ -839,7 +839,7 @@ pthread::cancel ()
       ioctl ()
       link ()
       linkat ()
-    o lio_listio ()
+    * lio_listio ()
       localtime ()
       localtime_r ()
     * lockf ()