Changing units of stiffness parameter in classical (new) SPH solver: used to be speed of sound squared; now just speed of sound.

The classical SPH solver was not in 2.65, so this change is unlikely to affect many users. But beta users who have been trying it out will need to change the stiffness parameter to sqrt(old value).


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53724 954f8c5b-7b00-dc11-b283-0030488c597c