Deadlock in the test suite

[alexcrichton]

Four builds recently have failed due to what appears to be deadlock. Two of them were on the master-linux builder while others were on various auto builders. This appears to happen during libstd tests or rpass tests:

• http://buildbot.rust-lang.org/builders/auto-mac-all-opt/builds/167/steps/test/logs/stdio
• http://buildbot.rust-lang.org/builders/master-linux/builds/199/steps/test/logs/stdio
• http://buildbot.rust-lang.org/builders/master-linux/builds/198/steps/test/logs/stdio
• http://buildbot.rust-lang.org/builders/auto-linux-64-opt/builds/184/steps/test/logs/stdio

[bblum]

Could be #3127. Not that that helps much.

[alexcrichton]

I believe that this may have just been swapping. This hasn't been seen recently, so closing.