fix for own regression [#34096] ocean sim vertex color bug
Caused by my assumption that alpha wasn't used for vertex colors.

Infact it is used by blender-internal rendering, but typically only for blending strand particles.
Updated comments to note this.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54481 954f8c5b-7b00-dc11-b283-0030488c597c