(The below text is no longer valid: netifaces has released a 64-bit
Python 2.7 wheel for Windows.  Ticket #3733 made the switch in CI.  We
should be able to test and run Tahoe-LAFS without needing vcpython27
now.)

Tahoe-LAFS CI now runs tests only on 32-bit Windows. Microsoft has
removed vcpython27 compiler downloads from their site, and Tahoe-LAFS
needs vcpython27 to build and install netifaces on 64-bit Windows.