According to the lactation specialist that conducted the breastfeeding class that I went to, a glass of wine or a beer or two will not affect the baby at all. Only when you consume it to the point where you are intoxicated. She also said that if you have an alcoholic beverage, you do not need to "pump and dump". Again, only if you drink enough to become intoxicated. I'm not saying that one should make a habit of drinking a glass each night, but I don't think one glass here and there will hurt you or the baby. Just be responsible. And if in doubt, just pump and dump.
Go for it!!! You deserve a glass after 9 months of pregnancy! Celebrate!!