masquerade 6.x-1.7

#987610: Notice: Undefined variable: _SESSION in masquerade_init
#1103588: Cleanup code and optimize query count
#1019832: masquerade_user_update doesn't check whether $edit['masquerade_users'] is set, data loss occurs
#1184996: Wrong operator in hook_user('update')
Changed attributes of README to 0644
#1147312: Notice: Trying to get property of non-object in masquerade_block_1()
Fixed alt_login module integration
#1007052: Fix update function, info file and block caching

Fix undefined variable notice, #git
#987610 by mikeytown2, hadsie: Fix instantiation in masquerade_init()
backport #1103588 isset()
backport of Issue #1019832 by bdragon: masquerade_user_update doesn't check whether ['masquerade_users'] is set, data loss occurs
Issue #1184996: Fix wrong operator in hook_user('update').
Changed attributes of README to 0644
Issue #1147312 by jason.fisher and andypost: Fix nitice in masquerade_block_1()
Fixed alt_login module integration
Issue #1007052 by andypost: Fixed update function, info file and block caching.