General Mills has been bitten by the bug infecting the consumer staples sector, but the weakness could be a buying opportunity for long-term investors.For a third consecutive year, consumer-packaged goods stocks will lag the S&P 500. The sector's weakness is so palpable that a screen of S&P 500 members yielding a minimum of 3% and down at least 10% this year yields 11 staple names. That's 11 out of 42 stocks that fit that bill.General Mills (GIS +1.03%) is one of those offenders and an egregious one at that ...