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);
}
Remove the unused extra gl param to waitForCompositor
Fix comments
Clean up code to use wtu.checkCanvas*()
Merge pull request #718 from zhenyao/rendering

Clean up code to use wtu.checkCanvas*()
Clean up tests: use wtu whenever appropriate.
Merge pull request #719 from zhenyao/clean

Clean up tests: use wtu whenever appropriate.
More cleanup: use wtf functions when possible.
Merge pull request #720 from zhenyao/clean

More cleanup: use wtf functions when possible.
Merge pull request #717 from zhenyao/wait

Remove the unused extra gl param to waitForCompositor
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