Slide effect slides docks to "fix" the problem when switching to a
virtual desktop that has a window in full screen mode:
As it turns out, people don't like this kind of behaviour. Another
problem with sliding of docks is that pager goes away.
This change disables sliding of docks by default. One can enable sliding
of docks by checking "Slide docks" checkbox in slide effect KCM.
Yet, transition to/from virtual desktop with a window in full screen
mode doesn't look great but that's somewhat acceptable: