Fix error
wait for server to die in teardown
Make stop command more robust, and use it in test
server.gets may be nil if eof, handle that
Check that STDIN is a tty
Rename method so we don't run it as a test
Ensure we collect all the output
Fix build with Ruby 2

test/unit in Ruby 2 is doing all sorts of fancy shit if stdout is a tty,
which messes up the test. So just use pipes for stdout and stderr. stdin
still needs to be a pty otherwise some output will end up in the
terminal where the spring tests are being run.

See also #58