[Fix] a crash on iOS 6 due to background tasks management

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
Use a copy of user identifier on alias method

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
Merge branch 'master' into refactoring

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>

Conflicts:
	Liquid/Liquid.m