Improve syntax error reporting; revert babel-runtime change.

[cpojer]

This diff makes a number of changes:

• It adds a useful message when a syntax error happens due to a configuration issue. This is something that a lot of people, including me, run into. There are a couple of scenarios that the new message should address:
  • babel-jest is installed but .babelrc is not properly set up. The code may use imports but it doesn't transform them into requires
  • no preprocessor is set up at all but people expect code to just work
  • the preprocessor was updated but the cache key doesn't consider everything and people don't know to use --no-cache.
  • it also prints the code that it tried to run. This is especially valuable for debugging – something I've run into dozens of times myself and I always had to hack Jest to print the source.
  • Screenshots: screenshot1 and screenshot2
  • Funny enough, the stack trace filter used to filter every line that contains node_modules. Since the message is part of the stack trace, it would filter out Preprocessor: node_modules/babel-jest. That took a while to figure out… I changed the stacktrace filter to look for \s+at in the beginning of the message.
  • Note: this error is not triggered when Babel finds a legit syntax error in the source code. When that happens, babel throws an error that is not based on SyntaxError, so it bypasses this check. This is actually nice – it means we can show this message only while people have trouble setting up their preprocessor.
• We were swallowing runtime errors in --verbose mode, probably because @gaearon and I were working on the same code on the same time and after the merge of Haste2 #599 this got lost again. Unfortunately the reporter code is a bit unwieldy and hard to test – there is an internal task that tracks the rewrite of that component.
• This diff also removes babel-runtime again. It was added in Update babel-jest for better code coverage #785 but I had a chat with some of the babel core developers and it seems like the best course of action is to keep babel-polyfill. babel-runtime can be added by people who use babel-jest through .babelrc. Because Jest sets the NODE_ENV variable to test, it can be enabled just for the test environment as well. The auxiliaryCommentBefore option should be enough to fix code coverage reporting.

[cpojer]

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