ENH: Add math function for nearest power of two.

There are several places in VTK where the bounding power of two is
computed.  It is safer to centralize the code.  Use an O(log(N))
algorithm instead of the O(N) algorithm that was used before.

Change-Id: Idef2522d5a9357863837959975c0592751971010
ENH: Add math function for computing log2 on integers.

Computing log2() is useful for data partitioning algorithms.
This implementation works over the full 64-bit range.

Change-Id: I83fee61d06d6ce9c1b4afe30aedfe582ffa18ed7
ENH: More efficient Ceil() and Floor() with tests.

Change-Id: I7cedee87be08261b6e07b30547300814d024c6b5
Merge topic 'nearest-power-of-two' into master

067c578e ENH: More efficient Ceil() and Floor() with tests.
14865174 ENH: Add math function for computing log2 on integers.
93f35796 ENH: Add math function for nearest power of two.