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