Rename qAbs Function for timeval

This decouples it from qAbs which is declared as a constexpr under
certain compilation flags and enables for qtbase to be compiled with
GCC 4.8

Change-Id: I78e02256ffc8b460ca74ae5241e77dfac4e09ba9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Transient QWindows centered; default-constructed geometry

Default-constructed geometry does not mean put the window at 0,0,
and it does not mean center the window on the screen: it means
let the window manager position the window.  If the window is
explicitly positioned at 0,0 though, that is a higher priority
than the transient hint; without this change, the transientFor property
had no effect.  On X11, transient means use center "gravity" to
make the transient window exactly centered.  But the user can still
override the geometry of a transient window, as with any window.
On OSX and Windows, neither transient window functionality nor smart
initial positioning are provided, so a window with no position set
will be centered on the screen, and a transient window will be put
at the center of its transientParent.

Change-Id: I4f5e37480eef5d105e45ffd60362a57f13ec55f5
Task-number: QTBUG-26903
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>