Error display: Show the stdout string when there was nothing on stderr. The output is suboptimal (especially when it's a build error that wasn't actually caused by the sketch code), but better than nothing.

I ran into this in a build error when ino couldn't find boards.txt. Possibly Arduino 1.5.2 related? I haven't investigated that part yet.
When boards.txt is missing, fill in our own, more useful, more actionable error message.

It turned out that I was getting the missing-boards.txt message because that file moved (and has been split into two, one for avr and one for “sam”/ARM) in Arduino 1.5.2. So, until ino/ino-cocoduino knows how to work with that, this is the best Cocoduino can do.