[boost] Appveyor setup for msvc-14.1 toolset

Subject: [boost] Appveyor setup for msvc-14.1 toolset
From: Edward Diener (eldiener_at_[hidden])
Date: 2017-10-09 12:59:15

I have added an Appveyor test to some Boost libraries, but if I specify 
toolset=msvc-9.0,msvc-10.0,msvc-11.0,msvc-12.0,msvc-14.0,msvc-14.1 on 
the b2 test script command line the run fails when it gets to 14.1, due 
to not finding 'cl',  but succeeds for the others. What is the magical 
Appveyor incantation to test the latest VC++ ? I would like to avoid the 
environment/matrix gunk I see in other appveyor.yml files, but if it is 
the only way to get msvc-14.1 tests with Appveyor I will use it.