Added constant folding for relational (e.g. lessThan) built-ins, relational built-ins for uints, and bitwise ops for mixed scalars and vectors.

Also, allow comments to precede "#version 100".

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@23974 e7fa87d3-cd2b-0410-9028-fcbf551c1848