Book lovers, bargain hunters, and holiday shoppers: We're opening the doors once again this December for our hugely popular semiannual warehouse sale—with extended hours and two consecutive weekends, including Friday hours. Join us in Somerville for the Harvard Book Store Winter Warehouse Sale: » FIRST WEEKEND (Dec 6–8) Friday, December 6 (5pm–10pm) Saturday, December 7 (10am–8pm) Sunday, December 8 (10am–8pm) » SECOND WEEKEND (Dec 13–15) Friday, December 13 (5pm–10pm) Saturday, December 14 (10am–8pm) Sunday, December 15 (10am–8pm) Come explore thousands of remainders—fiction, cookbooks, children's books, comics,…