window-leak test fails when run via xvfb-run

[jamessan]

I was looking at updating Debian's x11-clipboard package from 0.8.1 to 0.9.x. I've tested all of 0.9.1 and 0.9.2. They both fail the window-leak test:

running 1 test
test tests::should_work_but_does_not ... FAILED

failures:

---- tests::should_work_but_does_not stdout ----
Error: XcbConnect(IoError(Os { code: 104, kind: ConnectionReset, message: "Connection reset by peer" }))

We use xvfb-run --server-args="-screen 0 1280x800x24" cargo test --all to run the tests, since the build environment doesn't have access to a typical X server.

This worked fine up through 3de406e but stopped working after that.