* Add rmdir, mkdir -p and umask to d8 on Unix.

      * Remove the non-working methods from the os object on d8 on Windows
so you can test for their presence with if (os.system).
* Add a test (not run by default since it only works on d8).
* Fix incorrect use of wait that left defunct processes (zombies).

Committed: http://code.google.com/p/v8/source/detail?r=1650

Review URL: http://codereview.chromium.org/56107

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@56276 0039d316-1c4b-4281-b951-d872f2087c98