Using structs with unary operators

Per section 5.7 of the GLSL ES spec, the only operators allowed on structs are field selector, equality and assignment. No unary operators are allowed.
This test verifies unary operators used on structures are disallowed.

Shader is of the form:
precision mediump float;
struct S { $(type) t; };
void main() {
    S a;
    a.t = $(initializer);
    S b = $(operator)a;   // Unary operators not allowed
    gl_FragColor = $(fragColor);
}
Address feedback from @zhenyao

- Fix misspelling: uary --> unary
- Add tests for ++ and -- unary operators.
Merge pull request #714 from RafaelCintron/structUnaryOperators

Using structs with unary operators