- hlsl.struct.frag variable changed to static, assignment replacd.
- Created new low level functions addBinaryNode and addUnaryNode. These are
used by higher level functions such as addAssignment, and do not do any
argument promotion or conversion of any sort.
- Two functions above are now used in RWTexture lvalue conversions. Also,
other direction creations of unary or binary nodes now use them, e.g, addIndex.
This cleans up some existing code.
- removed handling of EOpVectorTimesScalar from promote()
- removed comment from ParseHelper.cpp
