Add a spec covering the usage of the if function with call (#1588)
Add a spec covering the usage of the if function with call (#1588)

The if() function has a special evaluation behavior. But call() does not
have it and so calling if() through call() must not have this behavior.
sass/sass-spec,sass/sass-spec,sass/sass-spec,mgreter/sass-spec,sass/sass-spec,mgreter/sass-spec,mgreter/sass-spec