Misc. constant-folding fixes: Check % for 0, mat(mat) constructor, index range checking (within constant objects).  Also, rationalize addConst*() methods.
 

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@23973 e7fa87d3-cd2b-0410-9028-fcbf551c1848