Defect in XSH aio_error

[Geoff Clare <yyy@xxxxxxxxxxxxx>]

@ page 109 line 4025 section aio_error objection [gwc aio_error fails]

Problem:

Defect code :  2. Omission

The aio_error() and aio_return() pages are missing some text from
POSIX.1-1996 which defined their behaviour when the function fails.
(I.e. when the function itself fails, not the aio operation it is
reporting about.)

The relevant text from POSIX.1-1996 is:

    6.7.5.4 Errors
    [...]

    For each of the following conditions, if the condition is
    detected, the aio_error()  function shall return -1 and set errno
    to the corresponding value:  

    [EINVAL] The aiocbp argument does not refer [...]

    [...]

    6.7.6.4 Errors  

    If any of the following conditions occur, the aio_return()
    function shall return -1 and set errno to the corresponding value:  

    [EINVAL] The aiocbp argument does not refer [...]

Action:

Add after line 4025:

    If the aio_error() function fails, it shall return -1 and set
    errno to indicate the error.

For aio_return() on page 115 add after line 4232:

    If the aio_return() function fails, it shall return -1 and set
    errno to indicate the error.