[Truffle] Issue with getting backtick output

[bjfish]

Expected

ruby -e 'puts `/Users/brandonfish/Documents/jruby/bin/jruby -J-ea -J-Xmx2G -e "puts true"`'
true

Actual

 ruby -e 'puts `/Users/brandonfish/Documents/jruby/bin/jruby -X+T -J-ea -J-Xmx2G -e "puts true"`'

[bjfish]

This is need for the argf tests.

[chrisseaton]

The problem is that our File objects for stdout and stderr are not flushed on exit, as they're just normal objects - the runtime doesn't know anything about them. Minimal example of the problem:

$ jt e print 14 | wc
       0       0       0

[chrisseaton]

Fixed in 9e518a1