Fix pointer aliasing in kdtree
Fix pointer aliasing in kdtree

This commit addresses two problems related the the fast log2 computation in the kdtree :
* The code was written with Real = double in mind which may not always be the case. The variable is now explicitly set to double.
* GCC issues a warning for the reinterpret-cast when compiling with -fstrict-aliasing. The portable solution here is to use memcpy (according to http://dbp-consulting.com/tutorials/StrictAliasing.html) which compilers will optimize.
janbender/PositionBasedDynamics,janbender/PositionBasedDynamics,Gfans/PositionBasedDynamics,InteractiveComputerGraphics/PositionBasedDynamics,Gfans/PositionBasedDynamics,InteractiveComputerGraphics/PositionBasedDynamics,InteractiveComputerGraphics/PositionBasedDynamics