Okay, this one is quite odd.  It's definitely a timing issue.

If I put a `import time; time.sleep(1)` at the beginning of test_retrlines_too_line() -- i.e. first line of the method -- then the test reliably passes.  If I put a `print(len(line))` just before the maxline test in FTP.retrlines(), then the test will pass just as reliably.

If I put that retrlines() print *after* the maxline test, then it passes sometimes and fails sometimes.  When if fails, it's only ready 12 bytes from the `fp.readline()` call.  When it passes, it's reading 8193 bytes (thus triggering the expected exception).

I really hate to put a sleep in the test to make it pass.  Obviously it would be better not to fudge this race condition, but I don't know the code well enough to know where the race is yet.