Lockscreen : Previous screen fix

This attempts to fix : http://goo.gl/7esIV

This was added by : 01ad2f4a

I need to look into this some more, but if i can get feedback stating
that this indeed does have an effect, then it is something to look into.

Patchset2 : Change default from SHOW_SECURITY to SHOW_SLIDE

Patchset3 : Revert patchset 2

Change-Id: I96b0e94521e9598d1b24611c4132d9b77375c3f6