Fix bug: Scroll Effect issues in Workspace

Repro:
 - Set HomeScreen Scroll Effect to Flip or Stack
 - Create at least 3 pages in HomeScreen
 - Switch rapidly back and forth between pages
 - Observe certain pages will be transparent

Change-Id: I405a113fb947b193706d10921c2cf6ee7bb82b4f
Merge "Fix bug: Scroll Effect issues in Workspace" into cm-11.0
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_packages_apps_Trebuchet into kk4.4