Improve error reporting

[dspinellis]

Consider the following error report.

ERROR: No solution was found to satisfy the I/O requirements of the participating processes.dgsh-wrap: dgsh negotiation failed for /usr/bin/perl /home/dds/libexec/dgsh/dgsh-merge-sum with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/uniq -c with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/tr -s  \t\n\r\f with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/uniq -c with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/tr -s  \t\n\r\f with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/uniq -c with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/tr -s  \t\n\r\f with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/uniq -c with status code 4

dgsh-wrap: dgsh negotiation failed for /usr/bin/tr -s  \t\n\r\f with status code 4

dgsh-tee: dgsh negotiation failed with status code 4

The first line should offer more explanations. The remaining lines should not be outputted.