ruby2: fix fds.

[robbat2]

One of the Ruby 1.9->Ruby 2 upstream changes was that the handling of file descriptors on exec calls had two changes in defaults:

• All non-primary FDs are closed by default
• All FDs have CLOEXEC/close_on_exec set: http://ruby-doc.org/core-2.2.0/IO.html#method-i-close_on_exec-3D

Fixes formorer/pwstore#3

Signed-off-by: Robin H. Johnson [email protected]