unknown +variant silently ignored

[Craig Treleaven]

> On Jan 3, 2018, at 2:34 PM, Jan Stary <hans at stare.cz> wrote:
> 
> I just built "bitcoin +qt5", only to realize its "bitcoin +gui".
> While build the noneexistent +qt5 variant, the default variant
> was buit (which happens to be +daemon+wallet).
> 
> Is it intentional that a nonexistent variant is _silently_ ignored?
> Wouldn't it be less surprising if MP stopped with an error?
> Currently, a typo can result in something the user didnt want,
> eventhough it was easily avoidable.
> 
The variant specification is passed down to any dependencies that will be installed.  The current port can’t error out since that variant may be valid to one or more of the deps.  

Craig