Added support for passing existing MongoDB Objects for DB connectivity
Merge branch master from hillct
do not open the db if it is already open when passing a db instance, added tests
removed unnecessary check
Add support for Write Concern (merges https://github.com/kcbanner/connect-mongo/pull/48)
Ugrade to mongodb driver 1.2.x.
Merge remote-tracking branch 'mihs/master'
Removed test for clearing expired cookies as it isn't needed with the new TTL sessions.
Merge branch 'upgrade-to-mongodb-1.2.x'

Conflicts:
	lib/connect-mongo.js
	test/connect-mongo.test.js
Fixed WriteContern and test.