Output error on build failure.

[greghuc]

It's hard to debug anything running under broccoli-timepiece, as the output is just 'Build failed'.

This tiny pull request addresses this by also printing out the error. It's non-optional as (from personal experience) debugging is massively improved by having a clue as to what the problem is!

Example:

Build failed:

/vagrant/website/tmp/tree_merger-tmp_dest_dir-J17yFk7I.tmp/contact.coffee:22
  $(win.document).ready -> new Contact('#container', config.apiHost, config.homeUrl).start()
                                                                                            ^
ParseError: unmatched OUTDENT

I tested this by running it in an existing project using broccoli-timepiece. Works fine.

There is an existing pr that does something similar: https://github.com/rwjblue/broccoli-timepiece/pull/8. @piotrpalek sorry for not building on it, but this pull request is based on head, and is simpler.

Thanks!

[piotrpalek]

@greghuc np. I prefer simpler as well :) I just think there should at least be a switch to be able to turn "verbose mode" off.

[fourcube]

:+1:

[noyesa]

Can this get merged @rwjblue? I could have used more verbose error reporting from the start, which would have helped me figure out that I had an error from dependency mismatch, which is also solved by this PR. Thanks!

[sandstrom]

@greghuc this seems to be fixed on master. Would that work for your case as well? If so, feel free to close this PR.