Do *not* make file handles inheritable on Windows.

Do *not* make file handles inheritable on Windows.

This is the cause of the pub failures to unpack a file that has
just been created. The problem is that another 7-zip process has
inherited the file handle for a file that we are still writing.
When we are done writing the file, we cannot use it because the
other process still keeps the handle.

R=sgjesse@google.com,rnystrom@google.com
BUG=dartbug.com/5910

Committed: https://code.google.com/p/dart/source/detail?r=13960

[Søren Gjesse, 2012-10-23 13:01:17]

STV!

[Bob Nystrom, 2012-10-23 14:06:05]

Wow, fantastic detective work! Thank you thank you thank you!