BUG: Fix incorrect truncation to integer in vtkSlicerTransformLogic

The rotation was incorrectly truncated to integer.

This commit fixes the following clang warnings:

Slicer/Base/Logic/vtkSlicerTransformLogic.cxx:718:59: warning: using integer absolute value function 'abs' when argument is of
floating point type [-Wabsolute-value]
rotateArrow->RotateX(vtkMath::DegreesFromRadians(acos(abs(sliceNormal_RAS[2])))); // TODO: check this, it might not be correct for an arbi...
^

From: Hans Johnson <hans-johnson@uiowa.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24621 3bd1e089-480b-0410-8dfb-8563597acbee