make it obvious which log file has the error when dooplicity fails on a step in local/parallel modes

[nellore]

[BenLangmead]

I wish there were a global mechanism whereby individual tasks can report "catastrophic error 4675 happened and here's some text describing it," then some global process aggregates those, collapses identical errors from various task attempts, and reports it once to the user. "Catastrophic error 4675 reported by 45 task attempts". This global mechanism is essentially acting as a single command-line-style readout for warnings and errors, avoiding all the onerous drill-down.