Fix Warnings Level2

_See #2526_

Avoid [C4244](http://msdn.microsoft.com/en-us/library/2d7604yb.aspx) warnings, following [recommendations](http://randomascii.wordpress.com/2012/02/13/dont-store-that-in-a-float/) and [example](https://github.com/openframeworks/openFrameworks/blob/f2e909d081daa3fbcaa1a02d9721736d2e3e2092/libs/openFrameworks/math/ofMatrix4x4.h#L20).

**Fix Warnings Level-2**