#59 Async errors silently discarded

[Andreas Kupries]

In the current implementation of "comm" errors
happening in the receiver of a command are silently
discarded if the caller performed an -async invocation.

While that means that the caller itself is not
interested in a possible error I believe that it
should not be completely discarded. It makes
interactions based on async calls hard to debug as
problems simply show as the processes not doing what
they are supposed to do without any indication why
they are doing so.

The patch to be associated with this report will
extend the execution of received commands with a call
to [bgerror] (if available or loadable) so that such
errors do not get lost.

[Andreas Kupries]

Invoke bgerror for async errors

[Andreas Kupries]

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Committed to head, and version number bumped to 4.0 as
requested by John LoVerso (original author).