Optimize conditionals where the consequent and alternative are false and true

Optimize conditionals that return/assign true and false values.

Common examples:
````javascript
        if (y) {
            return true;
        } else {
            return false;
        }
        // will become return !!y;

        if (y) {
            x = true;
        } else {
            x = false;
        }
        // will become x=!!y;

        if (y) {
            x = false;
        } else {
            x = true;
        }
        // will become x=!y;

        x = y ? false : true;
        // will become x=!y;
````

Compressed and evaluated:
````javascript
// Before this change:
return y?true:false;x=y?true:false;x=y?false:true;x=y?false:true;
// or
return y?!0:!1;x=y?!0:!1;x=y?!1:!0;x=y?!1:!0;
// After this change:
return !!y;x=!!y;x=!y;x=!y;
````