Import r43724 from trunk by nobu

Gem::Util.popen should close open pipe to reap the child process, in 1.9
or later.  fix deadlock on waiting the child process whose output is
bigger than pipe buffer, in 1.8.
Import r43723 from ruby trunk by nobu

Discard output from git submodule

This patch breaks ruby 1.8 compatibility, a future patch will restore it
as preview2 is due shortly.