Issue #2298171 by AndrewBoag: Fixed Incorrect Message when non-existant user selected in masquerade block.

Issue #2211547 by David_Rothstein, DanChadwick, mrmikedewolf: Regression: RC6 checking for users in list prevents admin masqurade.

Issue #2211547 by David_Rothstein, DanChadwick, mrmikedewolf: Regression: RC6 checking for users in list prevents admin masqurade.

Issue #2211547 by DanChadwick, mrmikedewolf: Regression: RC6 checking for users in list prevents admin masqurade.

Issue #2087391 by iannakin: Fixed Notice when masquerading with alt_login() and PHP notices enabled.

Issue #1858862 by deekayen: Be more careful which which masquerade sessions get cleared when switching back.

Issue #1364574 by drumm, artkon, sheldonkreger: Invoke logout & login hooks for compatibility with bakery.

Issue #1293748 by jenna.tollerson: Fixed When site is offline, check permissions for 'Use the site in maintenance mode'.

Issue #1019832 by bdragon: masquerade_user_update doesn't check whether ['masquerade_users'] is set, data loss occurs

#1079312 by B-Prod: fix undefined key notice when page callbacks are missing (cherry-picking from commit 4e922767)

#1045306 by mariusz.slonina: Fatal error: Call to undefined method DatabaseStatement_sqlite::fetchColumn()