Added displaying of previous messages when user rejoins a room
Merge branch 'master' of ssh://athena.dialup.mit.edu/afs/athena.mit.edu/course/6/6.005/git/sp13/projects/guichat/alvarom-aybose-holliman
Merge branch 'master' of ssh://athena.dialup.mit.edu/afs/athena.mit.edu/course/6/6.005/git/sp13/projects/guichat/alvarom-aybose-holliman