Twitter has inadvertently revealed the date of its hugely anticipated IPO, reports Kurt Wagner for Mashable. The company filed an S-1 document that specified their employees would be allowed to sell their shares on the market from February 15, 2014. Since employees are normally barred from selling share for three months after an IPO, that sets November 15 as the big day. Companies normally leave that information out of the S-1 until they have announced the date and started pitching to big investors, so this is pretty clearly an accident. Even though Facebook Inc (NASDAQ:FB), Twitter’s most obvious competitor, had…