This function sets the AST error status to the value supplied.
It does not cause any error message to be produced and should
not be used as part of normal error reporting. Its purpose is
simply to communicate to AST that an error has occurred in some
other item of software.
For example, a source or sink function supplied as an argument
to astChannelastChannel or astFitsChanastFitsChan might use this to signal that an
input/output error has occurred. AST could then respond by
terminating the current read or write operation.