Issue #2619 has been updated by Hongli Lai.

File 0001-Add-method-Process.fork_supported-for-checking-wheth.patch added

Oops, I attached the wrong patch: the first one contains some local changes which I did not intend to include. Here's the correct patch.
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http://redmine.ruby-lang.org/issues/show/2619

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http://redmine.ruby-lang.org