Allow to see the output of the executed go subcommand

[ph]

I was helping a coworker to debug an issue with mage and we found that that it was a go path issue, but the output of mage was not really helpful since it just returned an exit status 1 error. To debug the situation I've enabled the dev log output from internal to output everything to stdout.

I believe it would be helpful if we could turn on that output using a flag or to output the result of the command when we are running in debug mode.

[natefinch]

running with -debug should output everything you could ever need... but it's certainly possible I missed a spot or two.