JUnit 4.7 test output is always buffered, lost if forked process exits abnormally

The junit47 provider and above support multi-threaded test execution, and thus interpose a buffering layer (ConcurrentReporterManager) in between the test output and the actual stderr/stdout. This is ostensibly to allow the multiple threads' stderr and stdout to be demuxed nicely when the suite completes. But, if the JVM exits abnormally (eg due to a segfault or a System.exit() call), no output is generated. This is problematic since it's very hard to debug the test failure!

In my opinion, the buffering layer should only be interposed when parallel running is enabled. For the non-parallel case, there's no need to buffer the output. A simple test case is to write a JUnit test which prints a line of output to stderr and then calls System.exit(1). The output doesn't show up anywhere.