Outputs created by child processes are not detected on WIndows 8

[zah]

On windows 8, tup doesn't seem to attach itself properly to spawned processes. Even the most simple test cases fail (see attached gist). This must be the real culprit behind my recent reopening of #80.

https://gist.github.com/3683701

git clone git://gist.github.com/3683701.git twin8 && cd twin8 && tup init && tup upd

 *** tup errors ***
tup error: Expected to write to file 'input.txt.out' from cmd 20 but didn't
 *** Command ID=20 ran successfully, but tup failed to save the dependencies.
 [ ] 100%
 *** tup: 1 job failed.

[WalkerCodeRanger]

I'm not able to reproduce this on Windows 7 using tup v0.7.6-18-gb22cb9e