Fix three real bugs and a pile of broken unit tests

[piki]

Added sanity checks for invalid :chdir (needed a new test) and fd => :close (fixed an existing test) options.

Stop ignoring SIGPIPE. Fixes two hung tests on OS X. Without this fix, yes runs forever instead of dying with SIGPIPE.

Protect dup'd fds from being closed on exec, in both pspawn and fspawn.

Removed a bashisms from 7 unit tests. They now pass with both dash (the default on modern Debian) and bash (still the default on OS X).

I have tested on:

• OS X 10.9.3 with Ruby 2.0.0
• Debian unstable with Ruby 1.9.3 and 2.1.2, and with /bin/sh symlinked to both dash and bash

[parkr]

This is splendid! :heart:

They run on my machine, too. Thanks a lot for the fixes, and for taking the time to look into this. You rock! :metal:

[tmm1]

Nice.

[piki]

@tmm1 :shipit:?