util: don't attempt to delete an open NamedTemporaryFile (fixes #440)
On Windows, I had problems both cloning and pulling new changes from the server.
The workaround was the clone/pull in WSL using Linux python. Not sure when this
broke, but apparently tempfile.NamedTemporaryFile has a lot of... limitations
on Windows.[1]
My suggestion of using mercurial.util.unlink() in the bug report didn't work
for pulling changes. I didn't test if it would have worked for cloning.
Note that this isn't a problem on the default branch, because support for
dulwich prior to 0.20 drops this code. It will generate a merge conflict, but
can be thrown away.