fix file handling bugs on windows. add util.posixfile class that has posix semantics on windows. fix util.rename so it works with stupid windows delete semantics.

#!/bin/sh

hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
touch b
hg add b
rm b
hg commit -A -m"comment #1" -d "1000000 0"