Testing everything on both Vibe and Phobos sockets is 90% redundant.

[Abscissa]

The Vibe/Phobos socket abstraction is pretty well encapsulated, has proved to be solid for several years, and I'm not aware of even one single time a test failure (beyond the basic connecting to a server) has ever been specific to one type of socket or the other.

Therefore, I don't think the entire test suite needs to be repeated for both Vibe and Phobos sockets anymore. When both Vibe and Phobos sockets are being tested, one of them can be reduced to a smaller set of "core" tests just to ensure the the sockets themselves are working (probably just making sure it can establish a connection to the server).

This would (safely) make a drastic reduction in testing time, and reduce unnecessary load on travis-ci.