Auto merge of #6707 - pcwalton:more-fds, r=larsbergstrom
Auto merge of #6707 - pcwalton:more-fds, r=larsbergstrom

script: Increase our file descriptor limit on Linux.

We've had problems with this before, and I think it's starting to cause
problems again.

See PRs #6629 and #6616; my current theory is that this is the problem.

r? @larsbergstrom

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